CI: initial NetworkManager autopkgtests

[slyon]

Description

We're testing NetworkManager from mantic-proposed against a local build of netplan.io from this repository.

So far we can only run NetworkManager's autopkgtests which allow for 'isolation-container'.

FR-4415

Checklist

• Runs make check successfully.
• Retains 100% code coverage (make check-coverage).
• New/changed keys in YAML format are documented.
• (Optional) Adds example YAML for new feature.
• (Optional) Closes an open bug in Launchpad.

[daniloegea]

I think it's fine hard coding mantic there. I though of using ubuntu-daily:devel so we wouldn't need to update the yaml, but I don't know if it's safe to use it...

[slyon]

I think it's fine hard coding mantic there. I though of using ubuntu-daily:devel so we wouldn't need to update the yaml, but I don't know if it's safe to use it...

Yes, that was my first attempt. But autopkgtest-build-lxd will then still create an autopkgtest/ubuntu/mantic/amd64 alias for the image, so we need to hard-code "mantic" anyway. Therefore, I decided to keep it the same in both places.