MRP-1763 ptlrpc: request status gets overwritten

That is why mdt_set_info() always return 0 to client
and lctl changelog_clear always exits with 0 event
when called with wrong changelog id.

lustre_msg_set_status() should be used only by
ptlrpc_send_reply(). It sets status from req->rq_status.

Change-Id: I8e515671715d45dec47cbe21746d267caaf43d94
Signed-off-by: Andriy Skulysh <andriy_skulysh@xyratex.com>
Reviewed-on: http://es-gerrit.xyus.xyratex.com:8080/1692
Tested-by: Jenkins
Reviewed-by: Alexander Boyko <alexander_boyko@xyratex.com>
Reviewed-by: Alexey Lyashkov <alexey_lyashkov@xyratex.com>
Reviewed-by: Vitaly Fertman <vitaly_fertman@xyratex.com>