LU-4796 osd: NOT inject OBD_FAIL_FID_LOOKUP on dotdot

The namespace LFSCK may cannot rebuild the FID-in-dirent for dotdot
entry after the MDT restored from file-level backup, because there
is not enough space in the directory head area.

Signed-off-by: Fan Yong <fan.yong@intel.com>
Change-Id: I06e8a56dc0a6522e12fd0dfd5b513c1dbf0a80f4
Reviewed-on: http://review.whamcloud.com/9748
Tested-by: Jenkins
Tested-by: Maloo <hpdd-maloo@intel.com>
Reviewed-by: Lai Siyao <lai.siyao@intel.com>
Reviewed-by: Alex Zhuravlev <alexey.zhuravlev@intel.com>
Reviewed-by: Oleg Drokin <oleg.drokin@intel.com>