Start testing on Fedora N+1 earlier

[jlebon]

We've hit a lot of issues in the Fedora 34 rebase of coreos-assembler (e.g. rpmdb change, QEMU NVMe related regressions). We need to get ahead of these issues so that we can work with maintainers earlier and fix them.

Following up on discussions in https://github.com/coreos/rpm-ostree/pull/2806, let's have a coreos-assembler:next tag to track this and e.g. use it for building FCOS rawhide? And also hook it up to openshift/os's CI as non-blocking to get RHCOS exposure as well.

[dustymabe]

I think it's the right thing to do, though to do it right we need to really keep up with it. It won't be an insignificant amount of time (daily, weekly) spent debugging issues. It will be valuable to us and the rest of Fedora.

Can we do it right?

[jlebon]

Yeah, agreed. This is why I suggested having at least rawhide built with it so we have an incentive to fix issues.

[jlebon]

We discussed this today. A sweet spot might be to start tracking cosa based on N+1 once N+1 branches. Content churns much less, and it's still ahead enough of the rebase to be able to test it well and fix/report whatever needs fixing before rebasing :main.

Ideally we keep it all in the main branch and don't have a e.g. branched branch that we need to keep in sync. Instead, build-cosa could provide a build arg, or alternatively override the --from and we can key off of VERSION_ID in cosa if we really need some logic conditional.