The setup should be container engine agnostic. This changes allows this script
to be run on systems which prefer docker over podman (e.g. Github Actions).
This does not yet actually upload the image, and it only supports empty
images. You need to place a an empty file named <filename>, with a valid
extension (e.g., .qcow2) in /mnt/koji/work/<directory>/.
Signed-off-by: Tom Gundersen <teg@jklm.no>
