LU-957 scrub: trigger OI scrub if found bad OI entry

LU-957 scrub: trigger OI scrub if found bad OI entry

If some RPC involves OI lookup and finds inconsistent OI mapping,
it should trigger OI scrub to check and repair the inconsistency.

Known issues:
When the fid is returned to client, the OI mapping corresponding
to such fid may be not updated, or not committed to disk yet. If
server crashed before OI scrub completed, then recovery with the
fid corresponding to inconsistent OI mapping may fail or blocked.

Signed-off-by: Fan Yong <yong.fan@whamcloud.com>
Change-Id: I9709386aa6d42954b619f6b1342adae59a2ec5a9
Reviewed-on: http://review.whamcloud.com/2554
Tested-by: Hudson
Tested-by: Maloo <whamcloud.maloo@gmail.com>
Reviewed-by: Alex Zhuravlev <bzzz@whamcloud.com>
Reviewed-by: Andreas Dilger <adilger@whamcloud.com>