LU-5506 lfsck: skip orphan MDT-object handling for failed MDTs

LU-5506 lfsck: skip orphan MDT-object handling for failed MDTs

The namespace LFSCK will record the failed MDTs in the LFSCK tracing
file (lfsck_namespace) during the first-stage scanning, then when it
moves to the second-stage scanning, it can know which (the failed)
MDT(s) contain the MDT-objects that may have un-verified name entries
on other MDTs. Then the LFSCK will skip the orphan MDT-objects
handling on those ever failed MDTs. But other MDTs can be handled as
normal case without affected by the failed MDTs.

Signed-off-by: Fan Yong <fan.yong@intel.com>
Change-Id: Ic53d2fa24f81fb918d130dbc27694d3b68dc19d6
Reviewed-on: http://review.whamcloud.com/11444
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: Andreas Dilger <andreas.dilger@intel.com>