Comment 1 for bug 1824217

Suggest adding function systemd_is_installed() and add another elif systemd_is_installed(): return service('is-active', service_name) before line https://github.com/juju/charm-helpers/blob/master/charmhelpers/core/host.py#L308 that checks. This would cover a more generic case of using the os-native tools on trusty before reverting back to systemd, but would cover both snap and non-snap systemd-only services installed on trusty.