LU-11456 mdt: mdt_object_sync() can skip sync

LU-11456 mdt: mdt_object_sync() can skip sync

if object's version is found committed. OST implements this logic yet.

Change-Id: I17a05c0202bba3f97f80b165d6a3c9c2aff01996
Signed-off-by: Alex Zhuravlev <bzzz@whamcloud.com>
Reviewed-on: https://review.whamcloud.com/33266
Reviewed-by: Andreas Dilger <adilger@whamcloud.com>
Tested-by: jenkins <devops@whamcloud.com>
Tested-by: Maloo <maloo@whamcloud.com>
Reviewed-by: Mike Pershin <mpershin@whamcloud.com>
Reviewed-by: Oleg Drokin <green@whamcloud.com>