QPID-5798: [Java Broker Tests] Intermittent failure of FailoverBehaviourTest due to race condition within test

Work by Andrew MacBean <andymacbean@gmail.com>

git-svn-id: https://svn.apache.org/repos/asf/qpid/trunk@1599809 13f79535-47bb-0310-9956-ffa450edef68