Wip rbd notify errors

I think we should continue hiding notify failures from callers of librbd to preserve the current behavior for now. It's a bit odd to get an error when e.g. the resize or snap protect succeeded, but clients which might not even care about the change have not noticed it.


Instead, notify_change() can wait for the watch timeout period so unresponsive watchers lose their watch or know they missed updates (once http://tracker.ceph.com/issues/9195 is done). With that in place, and ictx_check() calling watch_check() from http://tracker.ceph.com/issues/9196, it'll even be safe, so returning success will be entirely correct.