Changes for require_valid_service
Testing out some of these commands on the jobrunner boxes it seems like
the systemctl in use there (systemd 215) is too old to accept the
--value flag. This throws an error.
I also realized that requesting a service that doesn't exist DOES NOT
exit non-zero, but just shows LoadState=not-found.
Reviewers: demon, mmodell, dduvall, Release-Engineering-Team
Reviewed By: demon, Release-Engineering-Team
Differential Revision: https://phabricator.wikimedia.org/D760