invoke-rc.d: syntax error: unknown option "--skip-systemd-native"

[Corey Bryant]

On bionic, the --skip-systemd-native flag is not available by default for invoke-rc.d.

This can be seen by installing nova-api-metadata from the ussuri cloud archive:
sudo add-apt-repository cloud-archive:ussuri
sudo apt install nova-api-metadata

This is coming from the postinst (and prerm) scripts:
# grep -r skip-systemd
nova-api-metadata.postinst: invoke-rc.d --skip-systemd-native nova-api-metadata $_dh_action || true
nova-api-metadata.prerm: invoke-rc.d --skip-systemd-native nova-api-metadata stop || true

Related Lintian warning:
https://lintian.debian.org/tags/skip-systemd-native-flag-missing-pre-depends

--skip-systemd-native
Exits before doing anything if a systemd environment is detected and the requested service is a native systemd unit. This is useful for maintainer scripts that want to defer systemd actions to deb-systemd-invoke(1p)

To work around this warning:
sudo apt install init-system-helpers

I think the fix is to add a Pre-Depends as the Lintian describes, however I believe this has been this way all along and considering the line ends with "|| true" it is probably not an issue.