Configuration of remote administration has been fixed to reload/restart services and/or warn user if necessary

- bnc#893606
- According to the bugreport, Yast Runlevel just restarts display manager while it enables remote administration
- I've fixed the behavior in a way that it starts or reloads services as much as possible and if the display manager is already running, Yast warns user to restart it manually or log out and log in again
- Includes a  nice test case

maybe it is better to be more specific here. So explicitelly mention xinetd and display-manager so if someone in future complain that we do not touch service Y we can add it here and extend test. Otherwise it was not so obvious.