Extend logging for CheckBrokerChange

[adyach]

We had situations, when the broker was restarted without any clear reasons.
The change checks if the broker is running and registered in zk. I have assumption, that the broker was running normally, but the connection to zk was lost, which triggered restart of the broker, because it was not possible to check if it is registered or not.
So, I suggest to extend logging for the check in order to identify the reason of restarts.