[EJBCLIENT-78] if shutdown() is called remove the shutdown task if the s...

...hutdown task is not initiating the shutdown()
https://issues.jboss.org/browse/EJBCLIENT-78
Use case would be war packaging jboss-client.jar running in a non JBoss AS 7 container and being how deployed in which case a new classloader would be created and another thread registered as shutdown handler