LU-1187 mdt: add out handler for object update

LU-1187 mdt: add out handler for object update

Add object update handler on remote MDT. Because the RPC
only includes object updates, (no metadata operation), the
out_handler will skip MDD layer and call osd layer directly.

Signed-off-by: wang di <di.wang@intel.com>
Change-Id: I9d553145cedfffcbb26d839ed8c7d9cc0887ed86
Reviewed-on: http://review.whamcloud.com/4928
Reviewed-by: Mike Pershin <mike.pershin@intel.com>
Reviewed-by: Alex Zhuravlev <alexey.zhuravlev@intel.com>
Tested-by: Hudson
Tested-by: Maloo <whamcloud.maloo@gmail.com>
Reviewed-by: Oleg Drokin <green@whamcloud.com>