LU-8215 tests: sanity-benchmark/iozone should wait for space recovery

LU-8215 tests: sanity-benchmark/iozone should wait for space recovery

otherwise it may fail due to a transient state where the space confsumed
by the previous run hasn't recovered yet. this happens to tiny filesystems
used in local setups.

Change-Id: I04b3ce096621583629277c1e52c64a1551bc8ace
Signed-off-by: Alex Zhuravlev <alexey.zhuravlev@intel.com>
Reviewed-on: https://review.whamcloud.com/20499
Tested-by: Jenkins
Tested-by: Maloo <hpdd-maloo@intel.com>
Reviewed-by: Andreas Dilger <adilger@whamcloud.com>
Reviewed-by: James Nunez <jnunez@whamcloud.com>
Reviewed-by: Oleg Drokin <green@whamcloud.com>