This container can be pulled via:
  docker pull registry.opensuse.org/home/dcassany/elementalgit/containers/rancher/seedimage-builder:1.7.0-dev
  docker pull registry.opensuse.org/home/dcassany/elementalgit/containers/rancher/seedimage-builder:1.7.0-dev-9.20
  docker pull registry.opensuse.org/home/dcassany/elementalgit/containers/rancher/seedimage-builder:latest

Set DOCKER_CONTENT_TRUST=1 to enable image tag verification.