LU-1267 lfsck: rebuild LAST_ID

LU-1267 lfsck: rebuild LAST_ID

The /O/<seq>/LAST_ID records the last oid of the object allocated
within the sequence. The LAST_ID file can be crashed or missed as
the system running. The LFSCK for layout consistency verification
can detect the LAST_ID lost/crashed cases, and can rebuild it via
scanning the whole device.

This functionality is also part of LU-14 live replacement of OST.

Introduce lfsck_notify callback - the LFSCK events notification
channel from the LFSCK to the registered users (MDD/OFD).

Introduce new connection flag: OBD_CONNECT_LFSCK to indicate that
whether the target server (MDT/OST) supports online LFSCK or not.

Test-Parameters: testlist=sanity-scrub,sanity-lfsck
Signed-off-by: Fan Yong <fan.yong@intel.com>
Change-Id: Iee85056e2fda1ecba9424c9f0e822643e9f029a8