QPID-5132: HA crash in test_tx_join_leave caused by double delete of queue. 

Fix crash caused by double-delete of transaction queue when a broker joins while
a transaction is in progress.

- Ignore mode for non-participants in TX.
- Try/catch around queue & exchange deletion.
- Consistent use of QueueRegistry::get when queues are required.
- Remove unnecessary exchange delete warning.
- Remove HaBroker::delete, use realm@username when deleting queues.

git-svn-id: https://svn.apache.org/repos/asf/qpid/trunk@1522031 13f79535-47bb-0310-9956-ffa450edef68