QPID-6201: [Java Broker] HA use separate single thread executor to deliver JE state change events

git-svn-id: https://svn.apache.org/repos/asf/qpid/trunk@1635547 13f79535-47bb-0310-9956-ffa450edef68
QPID-6202: [Java Broker] Ensure AMQProtocolEngine#closeSession() completes closure even if AMQChannel fails to close cleanly

git-svn-id: https://svn.apache.org/repos/asf/qpid/trunk@1635548 13f79535-47bb-0310-9956-ffa450edef68