LU-4446 tests: block on layout lock fix up on sanityn:51c

LU-4446 tests: block on layout lock fix up on sanityn:51c

Fixed two problems: set fail_loc on MDS and block at layout lock
by writing the test file.

Signed-off-by: Jinshan Xiong <jinshan.xiong@intel.com>
Change-Id: I8028e855aad5882981a313fb28ec5b87f593832b
Reviewed-on: http://review.whamcloud.com/8789
Tested-by: Jenkins
Reviewed-by: Jian Yu <jian.yu@intel.com>
Tested-by: Maloo <hpdd-maloo@intel.com>
Reviewed-by: John L. Hammond <john.hammond@intel.com>
Reviewed-by: Oleg Drokin <oleg.drokin@intel.com>