Document how to log to syslog rather than file solr.log [JIRA: RIAK-3401]

[lucafavatella]

Riak KV supports enabling logging to syslog via configuration but such configuration appears not to affect yokozuna. Documentation on how to make Yokozuna's Solr log to syslog would be beneficial for users.

Yokozuna logs to solr.log and it appears the log4j properties cannot be changed.

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Riak KV 2.2.3 includes yokozuna 2.1.10,
that includes (a modified version of) solr 4.10.4,
that includes log4j 1.2.17,
that includes syslog support.

Recent solr still includes log4j 1.2.17.
Recent log4j 2.x (2.8.1) still includes syslog support.

Solr 4.10.4 includes some examples of log4j properties (1, 2, 3) - apparently logging to file and/or console.
Solr 6.5.0 has similar sample log4j property samples, some templated wrt log dir.

[lucafavatella]

Approach of instantiation of log4j properties file is documented at 4a6910e

[lucafavatella]

To me the least intrusive approach looks like not changing yokozuna, and just:

• Add two templates in https://github.com/basho-labs/ansible-riak/tree/develop/templates - one as a copy of the standard yokozuna log4j properties and another one being the one with syslog only (not sure whether the two may be combined for logging both to solr.log and syslog - input welcome);
• Add a mention of the above syslog log4j template in ansible-riak in the docs at docs.basho.com