LU-1187 mdt: directory remote open fix

LU-1187 mdt: directory remote open fix

Directory remote open continue as normal open, i.e. return the
remote fid to client, and client will send the open request to
the right MDT.

Set correct it disposition in mdt_open_by_fid.

Signed-off-by: wang di <di.wang@intel.com>
Change-Id: I32d5dee9cd1eac47787e2d85a5db1e164d2846d3
Reviewed-on: http://review.whamcloud.com/4934
Reviewed-by: Andreas Dilger <andreas.dilger@intel.com>
Tested-by: Hudson
Reviewed-by: Alex Zhuravlev <alexey.zhuravlev@intel.com>
Tested-by: Maloo <whamcloud.maloo@gmail.com>
Reviewed-by: Mike Pershin <mike.pershin@intel.com>