Major Description
Now the LogRoll may exit before WAL exit but we will still write some close event to WAL when shutting down RS. And for AsyncFSWAL, we will open a new wal writer when error occur. If LogRoller has already exited then AsyncFSWAL will wait for ever and cause RS to hang.
It does not make sense to quit LogRoller ahead of WAL, this jira aims to change the shutdown order.