QPID-5820: [Java QMF2 Plugin] changes to plugin owing to the Java Broker model updates made during 0.29

* VHNs (virtualhostnodes) may exist within a VH (virtualhost)
* Use Port#availableProtocols rather than Port#protocols when trying to find the AMQP port
* Like the CPP Broker, Binding#arguments will be null if the binding was created with none.

Note that the QMF plugin still does not support virtualhosts created at runtime.  They'll be ignored until
the next restart.

Work done by Andrew MacBean <macbean@apache.org> and me.

git-svn-id: https://svn.apache.org/repos/asf/qpid/trunk@1606812 13f79535-47bb-0310-9956-ffa450edef68