Request for improved FailoverTransport logging

This is a request for improved logging based on a recent production outage that could have been identified and resolved much faster with better logging in the FailoverTransport.

Cluster update notifications are not logged. These are important, hopefully infrequent events and should be logged at INFO level in the updateURIs method:

https://github.com/apache/activemq/blob/master/activemq-client/src/main/java/org/apache/activemq/transport/failover/FailoverTransport.java#L1279

The exception that gives the cause of the failure to failover is logged at DEBUG level. This hid the root cause of the problem from us until we managed to figure out that additional information was available but hidden, and we turned up the logging level of the running client to DEBUG. Please turn this log line up to ERROR:

https://github.com/apache/activemq/blob/master/activemq-client/src/main/java/org/apache/activemq/transport/failover/FailoverTransport.java#L1279

Hopefully these are really trivial changes that you can make that will definitely enhance the operational transparency of the running clients.