This container can be pulled via:
  docker pull registry.opensuse.org/home/dcassany/staging/containers/rancher/seedimage-builder:1.9.0-rc1
  docker pull registry.opensuse.org/home/dcassany/staging/containers/rancher/seedimage-builder:1.9.0-rc1-4.16
  docker pull registry.opensuse.org/home/dcassany/staging/containers/rancher/seedimage-builder:latest

Set DOCKER_CONTENT_TRUST=1 to enable image tag verification.