Speedup Security.ReadServiceSettings (bnc#890349) 

* Greatly speed up the startup of yast-users and yast-security by avoiding 3 unnecessary calls to SystemdService.all
* Drop use of deprecated Service.EnabledServices
* Drop obsolete runlevel parameter from some methods
* Some basic tests
So what is the argument? You're passing number (3 or 5), but treat enabled_services as array?