LU-1291 mds: Test failure on test suite replay-single 44c

The obd_notify needs protect by mds_notify_lock. Else LOV
maybe gone while __mds_lov_synchronize be called.

Signed-off-by: yang sheng <ys@whamcloud.com>
Change-Id: Icb856b2a2b135711fd5681b0b4ebef0a1d78b988
Reviewed-on: http://review.whamcloud.com/2708
Reviewed-by: Niu Yawei <niu@whamcloud.com>
Reviewed-by: Johann Lombardi <johann@whamcloud.com>
Tested-by: Hudson
Tested-by: Maloo <whamcloud.maloo@gmail.com>
Reviewed-by: Andreas Dilger <adilger@whamcloud.com>