Potential lock unavailable due to dangling ephemeral nodes left during local session upgrading

There is a race condition which might be triggered if the client create session, upgrading the session with ephemeral node, then immediately issued close session request before it's removed from local session tracker.
 
The close session request will be treated as a local session close request since it still exists in the local session tracker, which goes through the ZK pipeline and delete the session from both local and global session tracker. Since the session is not tracked anymore, it will leave the ephemeral nodes there.