Inconsistent handling of System.exit in HostController's Main class

The org.jboss.as.host.controller.Main class has a couple abort() methods that deal with terminating the process while sending a proper exit code, and then a couple other places where System.exit() is called directly.

This should be cleaned up and handled consistently. Care must be taken though to ensure that the exit code that ends up being emitted isn't changed from the current behavior (unless their is clearly a bug in the current behavior.)