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

After refactoring in a834c34c3ca8d519911500e0a739ed766af2ddba ```@xinetd_installed``` is used only in this method so no need for ```@```