Fixes #5451: Add systemd support to Techniques

Ticket: http://www.rudder-project.org/redmine/issues/5451

To be merged in master
I think this class should be wider: it is at least ```SuSE|redhat```, since you define those explicitely above, but I think it will just work on any system with ```systemctl_installed```. So it should be ```systemctl_installed|SuSE|redhat```, IMHO.