Fixes #5633: Enable systemd support in ncf

Ticket: http://www.rudder-project.org/redmine/issues/5633

To be merged in master
Because it is functionally a different thing. The other methods make changes, this method just checks. So here, a repaired class just means "we ran the command and it didn't fail", which is actually "success". The classes_copy method won't deal with that.