LU-3336 lfsck: regenerate lost layout EA

LU-3336 lfsck: regenerate lost layout EA

To find out orphan OST-objects, the LFSCK on OST side maintains
two bitmaps in RAM for the OST-object accessed during the LFSCK.
After the first cycle system scanning, the LFSCK got the bitmap
for the known OST-objects, and got another bitmap for which OST
objects have been referenced by MDT-objects. Then the LFSCK can
know which OST-objects are not referenced by any MDT-object via
comparing the two bitmaps.

If the MDT-object exists, then check the layout EA. If related
layout EA is empty, then fill the layout EA slot with the given
OST-object stripe information. If the given OST-object stripe
index exceeds current layout EA size, then extend the layout EA
and fill the gap slot(s) as empty, which can be filled by others.

Signed-off-by: Fan Yong <fan.yong@intel.com>
Change-Id: Ie542289b397576be457b04792e845324d6926836
Reviewed-on: http://review.whamcloud.com/7810
Tested-by: Jenkins
Reviewed-by: Alex Zhuravlev <alexey.zhuravlev@intel.com>
Tested-by: Maloo <hpdd-maloo@intel.com>
Reviewed-by: Andreas Dilger <andreas.dilger@intel.com>
Reviewed-by: Oleg Drokin <oleg.drokin@intel.com>