LU-1187 osp: add osp_md_object for remote directory.

LU-1187 osp: add osp_md_object for remote directory.

In declare phase, the update for remote object will be added
in the remote list of the transaction, which will then being
sent to the remote MDT during trans_start.

Add osp_md_object for remote directory, any updates for
remote operation will be packed into RPC by api in
the osp_md_object

Signed-off-by: wang di <di.wang@intel.com>
Change-Id: I5fac24e21e6663dca0e2d2fa5d90d4a07a002136
Reviewed-on: http://review.whamcloud.com/4927
Reviewed-by: Mike Pershin <mike.pershin@intel.com>
Reviewed-by: Alex Zhuravlev <alexey.zhuravlev@intel.com>
Tested-by: Hudson
Tested-by: Maloo <whamcloud.maloo@gmail.com>
Reviewed-by: Oleg Drokin <green@whamcloud.com>