JBTM-2272 fix for 4.17

ISE failure in CDI transactional observer methods with remote EJB call using JTS

NO_TEST
@stuartwdouglas Thanks for pointing it out ! That's maybe a problem. I'm not sure the failing means the _theClassLoader will be null or there will be thrown an exception by getContextClassLoader() ?
sorry, I'm not similar with the security manager.
@tomjenkinson how do you think about this ?