LU-3336 lfsck: use rbtree to record OST-object accessing

LU-3336 lfsck: use rbtree to record OST-object accessing

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.

Above two bitmaps are organized via a single rbtree. The rbtree
is maintained by LFSCK on the OST side. For every LFSCK scanned
OST-object, it will be recorded in the known-bitmap, for every
OST-object accessed by any RPC during the scanning, it will be
recoreded in the accessed-bitmap.

Signed-off-by: Fan Yong <fan.yong@intel.com>
Change-Id: If399584a8617e7c368e48922a3582294ac98d5f4
Reviewed-on: http://review.whamcloud.com/7743
Tested-by: Jenkins
Reviewed-by: Andreas Dilger <andreas.dilger@intel.com>
Reviewed-by: Alex Zhuravlev <alexey.zhuravlev@intel.com>
Tested-by: Maloo <hpdd-maloo@intel.com>
Reviewed-by: Oleg Drokin <oleg.drokin@intel.com>