kola: Use github container registry for test images

[jepio]

Use github container registry for test imagees

We're hitting dockerhub pull rate limits in our CI. Most frequently it occurs with busybox and nginx images so I've mirrored those first. The nginx one is probably going to be pulled most often: the kubeadm tests run for 3 CNIs and multiple nodes each.

The mirroring was done with the following script:

#!/bin/bash

image=$1

platforms=( amd64 arm64 )
tags=()

for platform in "${platforms[@]}"; do
  var=$(docker pull $image --platform=$platform -q)
  tag=ghcr.io/kinvolk/$image:latest-$platform
  docker tag $var $tag
  docker push $tag
  tags+=( $tag )
done

docker manifest create ghcr.io/kinvolk/$image:latest "${tags[@]}"
docker manifest push --purge ghcr.io/kinvolk/$image:latest

Testing done

./bin/kola run --channel=alpha cl.internet docker.selinux

[tormath1]

LGTM ! Thanks :)