CLONE - HornetQ cluster with collocated backup serve cannot be shutdown gracefully

A bug was discovered which caused a node in HornetQ clusters using collocated back up servers to 'hang' indefinitely when sent the shutdown signal. This was caused by the JBoss Shutdown Hook thread being blocked from joining a <literal>JMSServerManagerImpl</literal> thread, because it, in turn, was waiting for a lock that was already held by the JBoss Shutdown Hook thread. This issue was corrected by changing the synchronization semantics of the related methods and by changing the order of operations. HornetQ cluster nodes now shut down gracefully when collocated.