Provide mechanism for knowing when running in-container

Whenever the jbossws code needs to know if it's running in-container or not, it currently rely on classloader checks to see if JBoss Modules is being used or not. That is fragile and fails to give reliable info when jboss modules is started for running standalone clients.
We hence need a better solution, perhaps based on some class that's started as part of the AS boot only.