LU-5208 tests: inject failure on the proper OST

LU-5208 tests: inject failure on the proper OST

The old test scripts assumed that the file created by the MDS2 will
be striped to the OST2 and OST1, but such assumption is wrong. When
the OSTs reside on different OSS nodes, the sanity-lfsck test_18c
will get failure.

Signed-off-by: Fan Yong <fan.yong@intel.com>
Change-Id: I755370e6a70384b5a70e046b1acc806e63817f6e
Reviewed-on: http://review.whamcloud.com/11275
Tested-by: Jenkins
Reviewed-by: James Nunez <james.a.nunez@intel.com>
Tested-by: Maloo <hpdd-maloo@intel.com>
Reviewed-by: Andreas Dilger <andreas.dilger@intel.com>