QPID-5409:  Add functionality to monitor for additions/removals from the group.  Add functionality
for RemoteReplicationNodes to montior themselves in order that their attributes reflect the state.

Also changed commit thread wrapper to abort any remaining commit futures on stop.

git-svn-id: https://svn.apache.org/repos/asf/qpid/branches/java-broker-bdb-ha@1558844 13f79535-47bb-0310-9956-ffa450edef68