LU-8753 osp: add rpc generation

LU-8753 osp: add rpc generation

Add rpc generation to make sure current update
request will not be sent until the remote llog
object got refresh.

Signed-off-by: Di Wang <di.wang@intel.com>
Change-Id: Iae678686b522d545b69510444805a1e411acfcfe
Reviewed-on: https://review.whamcloud.com/24364
Reviewed-by: Fan Yong <fan.yong@intel.com>
Tested-by: Jenkins
Tested-by: Maloo <hpdd-maloo@intel.com>
Reviewed-by: Andreas Dilger <andreas.dilger@intel.com>
Reviewed-by: Oleg Drokin <oleg.drokin@intel.com>