Fix and test for: https://issues.apache.org/jira/browse/AMQ-4505

When a broker was stopping it was sending out a cluster update after tearing down its bridges so any client connected to it would lose its awareness of other brokers in the cluster. 

git-svn-id: https://svn.apache.org/repos/asf/activemq/trunk@1478835 13f79535-47bb-0310-9956-ffa450edef68