Throughput mode only generates one results.csv regardless of how many subtests are run

[malucius-rh]

Description:
When running the iozone wrapper in throughput mode with more than one subtest (incache, incache+fsync, incache+mmap) enabled, the results.csv file left behind only contains results from the last subtest run.

Reproduction:

1. Run the iozone wrapper in throughput mode (not using --auto) with the --all_test option (which runs all available subtests, currently the three listed above)
2. When the run completes, examine the raw output files (there should be one for each subtest)
3. Examine the results.csv file
4. Observe: Only the results from the last completed subtest are included in the file

Expected behavior:
Results for all subtests run are in the results.csv file

Actual behavior: Only the last subtest's results are in the results.csv file

Example:
root@redacted# grep "Throughput " Run_1/xfs/*
Run_1/xfs/iozone_test_run_incache+fsync_default_dn_1.iozone: Throughput test with 1 process
Run_1/xfs/iozone_test_run_incache+fsync_default_dn_1.iozone: Child[0] xfer count = 10485760.00 kB, Throughput = 1800724.00 kB/sec
Run_1/xfs/iozone_test_run_incache+fsync_default_dn_1.iozone: Throughput test with 1 process
Run_1/xfs/iozone_test_run_incache+fsync_default_dn_1.iozone: Child[0] xfer count = 10485760.00 kB, Throughput = 5232825.00 kB/sec
Run_1/xfs/iozone_test_run_incache+mmap_default_dn_1.iozone: Throughput test with 1 process
Run_1/xfs/iozone_test_run_incache+mmap_default_dn_1.iozone: Child[0] xfer count = 10485760.00 kB, Throughput = 1460503.38 kB/sec
Run_1/xfs/iozone_test_run_incache+mmap_default_dn_1.iozone: Throughput test with 1 process
Run_1/xfs/iozone_test_run_incache+mmap_default_dn_1.iozone: Child[0] xfer count = 10485760.00 kB, Throughput = 5176744.50 kB/sec
Run_1/xfs/iozone_test_run_incache_default_dn_1.iozone: Throughput test with 1 process
Run_1/xfs/iozone_test_run_incache_default_dn_1.iozone: Child[0] xfer count = 10485760.00 kB, Throughput = 1825711.50 kB/sec
Run_1/xfs/iozone_test_run_incache_default_dn_1.iozone: Throughput test with 1 process
Run_1/xfs/iozone_test_run_incache_default_dn_1.iozone: Child[0] xfer count = 10485760.00 kB, Throughput = 5056195.50 kB/sec
[root@redacted# cat results.csv
processes:test_type:file_sze:record_size:Total_througput
1:initial writers:10485760 kB:Record Size 1024 kB: 1460503.38 kB/sec
1:readers:10485760 kB:Record Size 1024 kB: 5176744.50 kB/sec