LU-2736 mdd: remote dir rename under the same directory.

For "mv src_p/src_c tgt_p/tgt_c", src_c are remote directory,
if src_p and tgt_p are the same directory, and tgt_c does not exist,
this should be allowed, because all the modification will happen on
the single MDT where the parent is.

Test-Parameters: mdscount=2 mdtcount=2
Signed-off-by: wang di <di.wang@intel.com>
Change-Id: Ie7945933199648aadb9dfe68f00acf32a12c824f
Reviewed-on: http://review.whamcloud.com/5294
Reviewed-by: Fan Yong <fan.yong@intel.com>
Tested-by: Hudson
Reviewed-by: Andreas Dilger <andreas.dilger@intel.com>