Add alpine unittests to ci

[holmanb]

Proposed Commit Message

test: Add alpine to ci

Cloud-init has Alpine Linux support, yet does not regularly test it.

Alpine is an attractive addition to the test matrix since it is easily
available to run in lxc, and it has several alternative components to test
against:

- busybox: non-GNU posix-compliant tools
- musl: libc alternative to glibc
- openrc: init system alternative to systemd

Additional Context

Blocked by #5119 and #5120. Once those land, unittests will pass on Alpine.

Both have landed, ready for review.

Merge type

• Squash merge using "Proposed Commit Message"
• Rebase and merge unique commits. Requires commit messages per-commit each referencing the pull request number (#<PR_NUM>)

[TheRealFalcon]

Looks like the job failed:
https://github.com/canonical/cloud-init/actions/runs/8668134702/job/23775704648?pr=5121

[holmanb]

Looks like the job failed:
https://github.com/canonical/cloud-init/actions/runs/8668134702/job/23775704648?pr=5121

It succeeded a few weeks back but after a rebase to fix a conflict this test started failing and I haven't taken the time to debug it.

[aciba90]

Thanks for adding support for unit tests on other platforms than Ubuntu!

Instead of using incus, introducing a new tool, what about using the new image server for lxd[1]?

We could add the image server by lxc remote add images https://images.lxd.canonical.com --protocol=simplestreams or switch the lxd snap channel to 5.21/stable, which contains the image server by default.

[1] https://discourse.ubuntu.com/t/new-lxd-image-server-available-images-lxd-canonical-com/43824

[holmanb]

Instead of using incus, introducing a new tool, what about using the new image server for lxd[1]?

We could add the image server by lxc remote add images https://images.lxd.canonical.com --protocol=simplestreams or switch the lxd snap channel to 5.21/stable, which contains the image server by default.

When I proposed this PR, that image server was not yet available to use, but I suppose managing one tool would be simpler than two. I can update it.

[TheRealFalcon]

If we're doing LXD (and since the job is still failing), https://github.com/canonical/setup-lxd could be an option too.

[holmanb]

@aciba90 @TheRealFalcon I have it working with the lxd Github Actions. Ready for re-review!

[TheRealFalcon]

LGTM!