Add a basic RHCOS upgrade test for kola run-upgrade

[jlebon]

All the basic framework is in place for this. Two bits of design discussions:

1. How to fetch the previous RHCOS build. Note that this is not the same thing as the previous cosa build, so it's not just a matter of adding cosa buildprep --qemu or something. We want the starting image to be the latest "released" one, because that's the one that's actually going to perform the upgrade. The literal previous build might in fact be completely broken.

   The --find-parent-image switch on FCOS automatically determines the latest release on the stream being tested. The equivalent for RHCOS I guess would be to parse the build ID to find the release stream, query the OCP release stream API for the latest build ID released, then download the qcow2 for that build ID from S3.

2. How to actually perform the upgrade (see: kola: add run-upgrade command mantle#1168 (comment)) -- but really, even just rpm-ostree rebase would be fine to start.

[cgwalters]

This was done in #1467