[WFLY-2345] Port Offset 0 does not work

When a port offset is specified in the socket binding group and the
socket binding has a port of 0, then the port offset is not used to
calculate the port instead port 0 is bound.

This pull request contains three changes:

 - fix `SocketBinding` to also do offset calculation when the port is 0

 - extend `ControllerInitializer` to allow specifing the port offset

 - add a test in `OtherServicesSubsystemTestCase`

Issue: WFLY-2345
https://issues.jboss.org/browse/WFLY-2345