LU-1187 mdd: a few missing stuff in MD stack for DNE.

LU-1187 mdd: a few missing stuff in MD stack for DNE.

1. Assign the index operation for the directory create
in declare phase, which is needed for creating the
object in OUT.

2. Declare dotdot insertion for remote directory creation,
so the insert update can be packed into RPC and send to
the remote MDT (out) to be executed.

3. Add hint to the object declare phase, by which OSP can
get some info during update RPC packing, like parent fid.

4. Separate lu_object_exists into lu_object_remote and
lu_object_exists, so it can check whether remote object
exists as well.

Signed-off-by: wang di <di.wang@intel.com>
Change-Id: Icb359443d9982ee8567af933c5def42dc51a3a7a
Reviewed-on: http://review.whamcloud.com/4930
Tested-by: Hudson
Reviewed-by: Andreas Dilger <andreas.dilger@intel.com>
Reviewed-by: Alex Zhuravlev <alexey.zhuravlev@intel.com>
Tested-by: Maloo <whamcloud.maloo@gmail.com>
Reviewed-by: Mike Pershin <mike.pershin@intel.com>