QPID-5754 : [Java Broker] Make state change operations methods rather than calls to setDesiredState

git-svn-id: https://svn.apache.org/repos/asf/qpid/trunk@1593264 13f79535-47bb-0310-9956-ffa450edef68
QPID-5754 : [Java Broker] close the qmf agent when the plugin is closed

git-svn-id: https://svn.apache.org/repos/asf/qpid/trunk@1593267 13f79535-47bb-0310-9956-ffa450edef68