Don't validate registry certificates when registry is disabled

Fixes https://bugzilla.redhat.com/show_bug.cgi?id=1559248

playbooks/common/openshift-cluster/upgrades/post_control_plane.yml

@@ -37,6 +37,7 @@
 
 # Poll for registry and router pods, redeploy registry certs if needed.
 - import_playbook: ../../../openshift-hosted/private/upgrade_poll_and_check_certs.yml
+  when: openshift_hosted_manage_registry | default(True)
 
 # Check for warnings to be printed at the end of the upgrade:
 - name: Clean up and display warnings