check-dbus-services: pass machine-readability options to systemctl

Otherwise, when running check-dbus-services manually, it will
launch a pager.

Reviewed-by: Sjoerd Simons <sjoerd.simons@collabora.co.uk>
Signed-off-by: Simon McVittie <simon.mcvittie@collabora.co.uk>
Differential Revision: https://phabricator.apertis.org/D3903