Migrate away from gcr.io/k8s-testimages repo

[BenTheElder]

/kind bug
kubernetes/k8s.io#1523

gcr.io/k8s-testimages is a legacy Google-owned GCR/AR repo. We should migrate to a community-owned AR registry.

See for example kubernetes/k8s.io#1523 (comment)

cloud-provider-openstack/cloudbuild.yaml

Line 12 in e2e1a5b

- name: gcr.io/k8s-testimages/gcb-docker-gcloud

/priority important-soon