This appears to be a problem that goes away with debhelper-compat (= 12). The following are openstack packages that provide systemd init scripts, and the output is from the stable/xena branches. I've tested installing various binary packges from these and everything so far that has debhelper-compat (= 12) has it's systemd init script enabled, and everything so far that has debhelper (>= 10~) or debhelper-compat (= 10) has it's systemd init script disabled.

$ find . -name control | xargs grep debhelper
./networking-l2gw/debian/control: debhelper-compat (= 12),
./horizon/debian/control: debhelper-compat (= 12),
./designate-dashboard/debian/control: debhelper-compat (= 12),
./sahara-dashboard/debian/control: debhelper-compat (= 12),
./aodh/debian/control: debhelper (>= 10~),
./openstack-trove/debian/control: debhelper-compat (= 12),
./vitrage/debian/control: debhelper-compat (= 10),
./heat-dashboard/debian/control: debhelper-compat (= 12),
./swift/debian/control: debhelper-compat (= 12),
./masakari/debian/control: debhelper-compat (= 12),
./sahara-plugin-vanilla/debian/control: debhelper-compat (= 12),
./watcher-dashboard/debian/control: debhelper-compat (= 12),
./murano-dashboard/debian/control: debhelper-compat (= 12),
./ovn-octavia-provider/debian/control: debhelper-compat (= 12),
./masakari-monitors/debian/control: debhelper-compat (= 12),
./designate/debian/control: debhelper (>= 10~),
./murano-agent/debian/control: debhelper-compat (= 12),
./barbican/debian/control: debhelper (>= 10~),
./networking-odl/debian/control: debhelper-compat (= 12),
./neutron/debian/control: debhelper-compat (= 12),
./ceilometer/debian/control: debhelper-compat (= 12),
./placement/debian/control: debhelper-compat (= 12),
./networking-bagpipe/debian/control: debhelper-compat (= 12),
./heat/debian/control: debhelper-compat (= 12),
./networking-sfc/debian/control: debhelper-compat (= 12),
./senlin/debian/control: debhelper-compat (= 12),
./ironic-inspector/debian/control: debhelper-compat (= 12),
./octavia/debian/control: debhelper-compat (= 12),
./keystone/debian/control: debhelper-compat (= 12),
./gnocchi/debian/control: debhelper-compat (= 12),
./octavia-dashboard/debian/control: debhelper-compat (= 12),
./ironic/debian/control: debhelper-compat (= 12),
./networking-baremetal/debian/control: debhelper-compat (= 10),
./cinder/debian/control: debhelper (>= 10~),
./magnum-ui/debian/control: debhelper-compat (= 12),
./murano/debian/control: debhelper-compat (= 12),
./ironic-ui/debian/control: debhelper (>= 10~),
./watcher/debian/control: debhelper-compat (= 12),
./mistral/debian/control: debhelper-compat (= 12),
./magnum/debian/control: debhelper-compat (= 12),
./neutron-vpnaas/debian/control: debhelper-compat (= 12),
./manila-ui/debian/control: debhelper-compat (= 12),
./trove-dashboard/debian/control: debhelper-compat (= 12),
./neutron-dynamic-routing/debian/control: debhelper-compat (= 12),
./glance/debian/control: debhelper (>= 10~),
./networking-bgpvpn/debian/control: debhelper-compat (= 12),
./zaqar/debian/control: debhelper-compat (= 12),
./manila/debian/control: debhelper-compat (= 12),
./neutron-fwaas/debian/control: debhelper-compat (= 12),
./networking-hyperv/debian/control: debhelper-compat (= 12),
./sahara/debian/control: debhelper-compat (= 12),
./zaqar-ui/debian/control: debhelper (>= 10),
./vmware-nsx/debian/control: debhelper-compat (= 12),
./nova/debian/control: debhelper-compat (= 12),