resolve ConnectorXBeanConfigTest, broker service needs to null more impls at shutdown to allow restart to find new impls of scheudaler etc. consequence of fixes for https://issues.apache.org/activemq/browse/AMQ-2620 and https://issues.apache.org/activemq/browse/AMQ-2568
activemq/trunk/activemq-core/src/main/java/org/apache/activemq/broker/BrokerService.java