LU-6231 osp: prepare OUT RPC after remote transaction start

LU-6231 osp: prepare OUT RPC after remote transaction start

According to our current transaction/dt_object_lock framework
(to make the cross-MDTs modification for DNE1 to be workable),
the transaction sponsor will start the transaction firstly, then
try to acquire related dt_object_lock if needed. Under such rules,
if we want to prepare the OUT RPC in the transaction declare phase,
then related attr/xattr should be known without dt_object_lock. But
such condition maybe not true for some remote transaction case. For
example:

For linkEA repairing (by LFSCK) case, before the LFSCK thread obtained
the dt_object_lock on the target MDT-object, it cannot know whether
the MDT-object has linkEA or not, neither invalid or not.

Since the LFSCK thread cannot hold dt_object_lock before the remote
transaction start (otherwise there will be some potential deadlock),
it cannot prepare related OUT RPC for repairing during the declare
phase as other normal transactions do.

To resolve the trouble, we will make OSP to prepare related OUT RPC
after remote transaction started, and trigger the remote updating
(send RPC) when trans_stop. Then the up layer users, such as LFSCK,
can follow the general rule to handle trans_start/dt_object_lock
for repairing linkEA inconsistency without distinguishing remote
MDT-object.

In fact, above solution for remote transaction should be the normal
model without considering DNE1. The trouble brought by DNE1 will be
resolved in DNE2. At that time, this patch can be removed.

Signed-off-by: Fan Yong <fan.yong@intel.com>
Change-Id: Ib2ed4c290c9ae12b6f544575aa5313f0dc83a5af
Reviewed-on: http://review.whamcloud.com/13710
Tested-by: Jenkins
Tested-by: Maloo <hpdd-maloo@intel.com>
Reviewed-by: wangdi <di.wang@intel.com>
Reviewed-by: Alex Zhuravlev <alexey.zhuravlev@intel.com>
Reviewed-by: Oleg Drokin <oleg.drokin@intel.com>