issue-542: support for mBean servers that rewrite the supplied ObjectName upon regi...

...stration

The JMXReporter doesn't pick up the ObjectName WebSphere is creating based upon the supplied ObjectName; hence the ObjectName used during unregistration is causing it to fail.

If you look at the jmx javadoc: http://docs.oracle.com/javase/7/docs/api/javax/management/MBeanServer.html#registerMBean(java.lang.Object,%20javax.management.ObjectName)
You can see that the registerMBean method returns an ObjectInstance, that will contain the correct ObjectName that should be used for the unregister.