QPIDJMS-9: some small cleanup, add some additional tests

git-svn-id: https://svn.apache.org/repos/asf/qpid/jms/trunk@1569560 13f79535-47bb-0310-9956-ffa450edef68
QPIDJMS-9: ensure to clear up fields for JMSXUserID, JMSXGroupID, JMSXGroupSeq when clearing properties

git-svn-id: https://svn.apache.org/repos/asf/qpid/jms/trunk@1569562 13f79535-47bb-0310-9956-ffa450edef68