7120365: DiffHBTest.java fails due to ConcurrentModificationException
Summary: The problem is from the server notification forwarder, it should use a copy of listener set to do iterate.
Reviewed-by: alanb
grant {
permission java.net.SocketPermission "*:*", "accept,connect,listen,resolve";
permission javax.management.MBeanServerPermission "*";
permission javax.management.MBeanPermission "*", "invoke";
permission javax.management.MBeanPermission "[domain:type=NB,name=2]", "addNotificationListener";
permission javax.management.MBeanPermission "*", "removeNotificationListener";
};