LU-13097 tests: set fail_loc on all MDS nodes for pdir tests

LU-13097 tests: set fail_loc on all MDS nodes for pdir tests

Set fail_loc on all MDS nodes for pdir tests, not only $SINGLEMDS.

Test-Parameters: trivial testlist=sanityn,sanityn,sanityn,sanityn
Test-Parameters: testlist=sanityn,sanityn,sanityn,sanityn,sanityn
Test-Parameters: testlist=sanityn,sanityn,sanityn,sanityn,sanityn
Test-Parameters: testlist=sanityn,sanityn,sanityn,sanityn,sanityn
Signed-off-by: Sebastien Buisson <sbuisson@ddn.com>
Change-Id: I80d935eae0b06e39712abfe48a56b8ce08537926
Reviewed-on: https://review.whamcloud.com/37145
Tested-by: jenkins <devops@whamcloud.com>
Tested-by: Maloo <maloo@whamcloud.com>
Reviewed-by: Andreas Dilger <adilger@whamcloud.com>
Reviewed-by: James Nunez <jnunez@whamcloud.com>