LU-1866 scrub: initial OI scrub

LU-1866 scrub: initial OI scrub

We will extend OI mapping usage (in OI directories/files) to
all the objects, except for the objects which are marked as
"LDISKFS_STATE_LUSTRE_NO_OI" or OST object.

The OI mappings for the server-side local files may become
invalid because of server-side file-level back/restore, or
server crash. Those files are necessary for server mount,
so related OI mappings must be checked and rebuilt before
they are really used. That is the initial OI scrub work.

Initial OI scrub is used for quickly checking and rebuilding
OI mappings for server-side local files during server mount.

Another change is about MDT_LAST_RECV_OID/OFD_LAST_RECV_OID.
Currently, we can just use the same OID for the "last_rcvd"
files on different targets. So merge the two OIDs as single
OID: LAST_RECV_OID, which also simplifies OI scrub work.

Signed-off-by: Fan Yong <fan.yong@intel.com>
Change-Id: Iddca4812d3c82ca43f1e852fd74475b11b6e6dea
Reviewed-on: http://review.whamcloud.com/4903
Reviewed-by: Alex Zhuravlev <alexey.zhuravlev@intel.com>
Tested-by: Hudson
Reviewed-by: Andreas Dilger <andreas.dilger@intel.com>
Tested-by: Maloo <whamcloud.maloo@gmail.com>