QPID-5409: Refactor BDB HA system tests to use management REST interfaces instead of JMX. Add new system tests for setting priority, quorum override and role

git-svn-id: https://svn.apache.org/repos/asf/qpid/branches/java-broker-bdb-ha@1564250 13f79535-47bb-0310-9956-ffa450edef68