LU-6635 lfsck: block replacing the OST-object for test

LU-6635 lfsck: block replacing the OST-object for test

For sanity-lfsck test_18e, sometimes, before the client wirte
happened, the layout LFSCK has already gone into the phase2
and replaced the new created OST-object with the old orphan
OST-object, then cause the subsequent check failure.

To resolve such trouble, we will hold the layout LFSCK when
replacing the new created OST-object until the client write
happened.

Signed-off-by: Fan Yong <fan.yong@intel.com>
Change-Id: Ia5be2cd2ea920fa02bb281ca5c59d8d252f3fd7b
Reviewed-on: http://review.whamcloud.com/18146
Tested-by: Jenkins
Tested-by: Maloo <hpdd-maloo@intel.com>
Reviewed-by: Andreas Dilger <andreas.dilger@intel.com>
Reviewed-by: Lai Siyao <lai.siyao@intel.com>
Reviewed-by: Oleg Drokin <oleg.drokin@intel.com>