CI: Use libpod/registry as container registry

This is to avoid pulling the official Docker registry image. Docker Hub
already has strict pull rate limits for unauthenticated users and will
soon lower them further [1]. The pull rate limits are already causing CI
jobs to occasionally fail.

[1] https://docs.docker.com/docker-hub/usage/

Change-Id: I8c61840d7c9eb49012979b830aa5986f3634ecaa

playbooks/kayobe-seed-base/overrides.yml.j2

@@ -1,5 +1,7 @@
 ---
 docker_daemon_debug: true
+# Use alternative registry image to avoid Docker Hub pull rate limit.
+docker_registry_image_full: "quay.io/libpod/registry:2.8.2"
 # Use the OpenStack infra's Dockerhub mirror.
 docker_registry_mirrors:
   - "http://{{ zuul_site_mirror_fqdn }}:8082/"

playbooks/kayobe-seed-upgrade-base/overrides.yml.j2

@@ -1,5 +1,7 @@
 ---
 docker_daemon_debug: true
+# Use alternative registry image to avoid Docker Hub pull rate limit.
+docker_registry_image_full: "quay.io/libpod/registry:2.8.2"
 # Use the OpenStack infra's Dockerhub mirror.
 docker_registry_mirrors:
   - "http://{{ zuul_site_mirror_fqdn }}:8082/"

playbooks/kayobe-seed-vm-base/overrides.yml.j2

@@ -1,5 +1,7 @@
 ---
 docker_daemon_debug: true
+# Use alternative registry image to avoid Docker Hub pull rate limit.
+docker_registry_image_full: "quay.io/libpod/registry:2.8.2"
 # Use the OpenStack infra's Dockerhub mirror.
 docker_registry_mirrors:
   - "http://{{ zuul_site_mirror_fqdn }}:8082/"