Run chkconfig enable/disable only when needed.  TODO, apply same logic to update-rc.d/systemd
Service module now knows a little more about systemd.  This module is
really due for some refactoring, but telling how a service is managed is
a little fuzzy anyway.  on a systemd system typoing the service will now
give you a rather systemd specific error which is somewhat suboptimal.
Better detection of whether a service is managed by systemd or not.