Add notification for pause/unpause instance

When pause/unpause instance, there are no notifications, this
will cause someone cannot know when pause/unpause operation
would be finished.

All other instance operations do have notifications. We should
also add notification support for those two operations.

Change-Id: I5b8cc33a5992f5f028a3220217dcf7a0288d150d
Closes-Bug: #1043861
Merge "Add notification for pause/unpause instance"