Ticket 47500 - start-dirsrv/restart-dirsrv/stop-disrv do not register with systemd correctly

Description:  If "systemctl" is available on the system, and the user is root, then
              use systemctl to start & stop the server.

https://fedorahosted.org/389/ticket/47500

Reviewed by: richm(Thanks!)
(cherry picked from commit ba00d4885b93f8cc8d6eb1460bd0b5019e4d2fc2)