LU-1187 mdt: return lock to client for remote dir.

In mdt_reint_open, MDT should return LOOKUP inodebit lock for
remote directory.

Signed-off-by: wang di <di.wang@intel.com>
Change-Id: Iaa7c6a13b71b627c5792f4b28bb3c5520b2132e5
Reviewed-on: http://review.whamcloud.com/5026
Tested-by: Hudson
Reviewed-by: Jinshan Xiong <jinshan.xiong@intel.com>
Tested-by: Maloo <whamcloud.maloo@gmail.com>
Reviewed-by: Andreas Dilger <andreas.dilger@intel.com>
Reviewed-by: Oleg Drokin <green@whamcloud.com>