Changes

jobs: delete ignition-dracut

It's been archived for a while now.

jobs: rename fcct to butane

Follows the upstream repo rename.

jobs: don't create jobs in folders

There's a bug in BlueOcean where a link to a job containing slashes will
not work:

https://issues.jenkins.io/browse/JENKINS-47604

Let's hack around this by not creating folders and just having the jobs
live at the top-level.

pod: use `coreos-ci-sa` serviceAccount when using `runAsUser`

That service account has `RunAsAny` caps.

This is a bit hacky. Ideally, this shared lib wouldn't hardcode things
specific to either CoreOS CI or the pipeline here and instead we'd store
this config in https://github.com/coreos/coreos-ci. This works though
because the FCOS pipeline doesn't use `runAsUser` at all.

pod: use serviceAccountName instead of serviceAccount

The latter is deprecated. It should still work at the k8s level, but
it's possible there's something going on with the Jenkins kubernetes
plugin not handling this correctly.

pod: set serviceAccount in podTemplate instead of YAML

Setting the `serviceAccountName` field in the pod YAML itself is not
working with the kubernetes plugin. I noticed that `podTemplate` also
supports specifying the `serviceAccount` directly. It's possible that
that key is used and any service account set in the pod YAML directly is
always overridden.

Let's try using that instead.