Block etcdv3 migration for supported configurations

roles/etcd_migrate/tasks/check.yml

@@ -1,4 +1,8 @@
 ---
+- fail:
+    msg: "Currently etcd v3 migration is unsupported while we test it more thoroughly"
+  when: not openshift_enable_unsupported_configurations | default(false) | bool
+
 # Check the cluster is healthy
 - include: check_cluster_health.yml