Update get_repo_attribute to take into account that attribute value can be 0 byte value (empty)

[boegel]

Fix for eessi check crashing when attribute value could not be determined:

$ attr -g ncleanup24 /cvmfs/software.eessi.io
Attribute "ncleanup24" had a 0 byte value for /cvmfs/software.eessi.io:

[ocaisa]

LGTM

[boegel]

Just to confirm, this fixes the bug we saw on Leonardo, eessi check doesn't crash anymore now, it just reports:

    ❌ ERROR Revision (client):  UNKNOWN

and

        ❌ ERROR Number of cache cleanups in last 24h:  UNKNOWN

Without this fix, it went down hard:

Details

$ eessi check
📦 Checking for EESSI repositories...
    ✅ OK /cvmfs/dev.eessi.io is available
    ✅ OK /cvmfs/riscv.eessi.io is available
    ✅ OK /cvmfs/software.eessi.io is available

🔎 Inspecting EESSI repository software.eessi.io...
    ✅ OK /cvmfs/software.eessi.io is available
    ℹ Revision (client):
    💻 Client cache:
        ℹ Path to client cache directory: /var/lib/cvmfs/shared
        ℹ Shared cache: yes
        ℹ Client cache quota limit: 4.8828125 GiB
        ❌ ERROR Required field 'Cache Usage' not found!
╭───────────────────────────────────────────────────────────────────────────────────────────────────────────────────── Traceback (most recent call last) ──────────────────────────────────────────────────────────────────────────────────────────────────────────────────────╮
│ /leonardo/home/userexternal/khoste00/venv-py311-eessi-cli/lib64/python3.11/site-packages/eessi/cli/check.py:282 in check                                                                                                                                                     │
│                                                                                                                                                                                                                                                                              │
│   279 │                                                                                        ╭────────── locals ──────────╮                                                                                                                                                │
│   280 │   repo = EESSI_SOFTWARE_REPO                                                           │ help = None                │                                                                                                                                                │
│   281 │   rich_print(f":magnifying_glass_tilted_right: Inspecting EESSI repository {repo}...") │ repo = 'software.eessi.io' │                                                                                                                                                │
│ ❱ 282 │   check_repo(repo=repo)                                                                ╰────────────────────────────╯                                                                                                                                                │
│   283                                                                                                                                                                                                                                                                        │
│                                                                                                                                                                                                                                                                              │
│ /leonardo/home/userexternal/khoste00/venv-py311-eessi-cli/lib64/python3.11/site-packages/eessi/cli/check.py:246 in check_repo                                                                                                                                                │
│                                                                                                                                                                                                                                                                              │
│   243 │   │                                                                                                                                                                                                                                                                  │
│   244 │   │   for other_check in specs.get('other', []):                                                                                                                                                                                                                     │
│   245 │   │   │   if callable(other_check):                                                                                                                                                                                                                                  │
│ ❱ 246 │   │   │   │   other_check(repo, indent_level=2)                                                                                                                                                                                                                      │
│   247 │   │   │   else:                                                                                                                                                                                                                                                      │
│   248 │   │   │   │   raise ValueError(f"{other_check} is not callable?!")                                                                                                                                                                                                   │
│   249                                                                                                                                                                                                                                                                        │
│                                                                                                                                                                                                                                                                              │
│ ╭───────────────────────────────────────────────────────────────────────────────────────────────────────────── locals ──────────────────────────────────────────────────────────────────────────────────────────────────────────────╮                                        │
│ │            cmd = 'cvmfs_config stat -v software.eessi.io'                                                                                                                                                                         │                                        │
│ │          descr = 'Client cache'                                                                                                                                                                                                   │                                        │
│ │      exit_code = 1                                                                                                                                                                                                                │                                        │
│ │          field = 'Cache Usage'                                                                                                                                                                                                    │                                        │
│ │   grouped_keys = {                                                                                                                                                                                                                │                                        │
│ │                  │   'Client cache': {                                                                                                                                                                                            │                                        │
│ │                  │   │   'sigil': 'computer',                                                                                                                                                                                     │                                        │
│ │                  │   │   'keys': ['CVMFS_CACHE_DIR', 'CVMFS_SHARED_CACHE', 'CVMFS_QUOTA_LIMIT'],                                                                                                                                  │                                        │
│ │                  │   │   'stat_fields': ['Cache Usage'],                                                                                                                                                                          │                                        │
│ │                  │   │   'other': [<function check_cache_cleanups at 0x150071f863e0>]                                                                                                                                             │                                        │
│ │                  │   },                                                                                                                                                                                                           │                                        │
│ │                  │   'Server/proxy settings': {'sigil': 'globe_showing_europe-africa', 'keys': ['CVMFS_SERVER_URL', 'CVMFS_HTTP_PROXY', 'CVMFS_USE_GEOAPI']},                                                                     │                                        │
│ │                  │   'Other': {'sigil': 'information_desk_person', 'keys': ['CVMFS_CLIENT_PROFILE']}                                                                                                                              │                                        │
│ │                  }                                                                                                                                                                                                                │                                        │
│ │            key = 'CVMFS_QUOTA_LIMIT'                                                                                                                                                                                              │                                        │
│ │          regex = re.compile('^Cache Usage:(?P<value>.*)', re.MULTILINE)                                                                                                                                                           │                                        │
│ │           repo = 'software.eessi.io'                                                                                                                                                                                              │                                        │
│ │      repo_path = '/cvmfs/software.eessi.io'                                                                                                                                                                                       │                                        │
│ │            res = None                                                                                                                                                                                                             │                                        │
│ │       revision = ''                                                                                                                                                                                                               │                                        │
│ │        setting = 'Client cache quota limit'                                                                                                                                                                                       │                                        │
│ │ setting_values = {'CVMFS_CACHE_DIR': '/var/lib/cvmfs/shared', 'CVMFS_SHARED_CACHE': 'yes', 'CVMFS_QUOTA_LIMIT': '5000'}                                                                                                           │                                        │
│ │          specs = {'sigil': 'computer', 'keys': ['CVMFS_CACHE_DIR', 'CVMFS_SHARED_CACHE', 'CVMFS_QUOTA_LIMIT'], 'stat_fields': ['Cache Usage'], 'other': [<function check_cache_cleanups at 0x150071f863e0>]}                      │                                        │
│ │    stat_output = ''                                                                                                                                                                                                               │                                        │
│ │         status = 'INFO'                                                                                                                                                                                                           │                                        │
│ │         stderr = ''                                                                                                                                                                                                               │                                        │
│ │          value = '4.8828125 GiB'                                                                                                                                                                                                  │                                        │
│ ╰───────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────╯                                        │
│                                                                                                                                                                                                                                                                              │
│ /leonardo/home/userexternal/khoste00/venv-py311-eessi-cli/lib64/python3.11/site-packages/eessi/cli/check.py:167 in check_cache_cleanups                                                                                                                                      │
│                                                                                                                                                                                                                                                                              │
│   164 │   if ncleanup24 == UNKNOWN:                                                            ╭──────────────────────── locals ─────────────────────────╮                                                                                                                   │
│   165 │   │   status = ERROR                                                                   │ indent_level = 2                                        │                                                                                                                   │
│   166 │   else:                                                                                │          msg = 'Number of cache cleanups in last 24h: ' │                                                                                                                   │
│ ❱ 167 │   │   ncleanup24 = int(ncleanup24)                                                     │   ncleanup24 = ''                                       │                                                                                                                   │
│   168 │   │                                                                                    │         repo = 'software.eessi.io'                      │                                                                                                                   │
│   169 │   │   if ncleanup24 > 24:                                                              ╰─────────────────────────────────────────────────────────╯                                                                                                                   │
│   170 │   │   │   status = WARNING                                                                                                                                                                                                                                           │
╰──────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────╯
ValueError: invalid literal for int() with base 10: ''