LU-6343 lfsck: locate object only when necessary

LU-6343 lfsck: locate object only when necessary

Currently, for every item to be verified by the LFSCK assistant
thread, the LFSCK assistant thread will try to locate its parent
directory (for namespace LFSCK) or its parent MDT-object (for
layout LFSCK) firstly via the given parent FID. But under most
cases, the system is consistent, such locating parent object is
unnecessary. For example, for namespace LFSCK, the LFSCK main
engine has put the <parent_FID, child_name, child_FID> in the
pre-loaded request, then the assistant thread will locate the
child object with the child_FID and search its linkEA to find
the <parent_FID, child_name> pairs.

Be as some improvement, we will make the LFSCK to locate related
object (especially for parent object) only when really used.

Signed-off-by: Fan Yong <fan.yong@intel.com>
Change-Id: If6a3677a6ad3fa1c694ee06f9688c1f38374f8de
Reviewed-on: http://review.whamcloud.com/13993
Tested-by: Jenkins
Tested-by: Maloo <hpdd-maloo@intel.com>
Reviewed-by: Alex Zhuravlev <alexey.zhuravlev@intel.com>
Reviewed-by: Lai Siyao <lai.siyao@intel.com>
Reviewed-by: Oleg Drokin <oleg.drokin@intel.com>