Rename refstack group variables

When we cleaned up the puppet in
I6b6dfd0f8ef89a5362f64cfbc8016ba5b1a346b3 we renamed the group
s/refstack-docker/refstack/ but didn't move the variables and some
other references too.

Change-Id: Ib07d1e9ede628c43b4d5d94b64ec35c101e11be8

playbooks/zuul/run-base.yaml

@@ -63,7 +63,7 @@
         - group_vars/meetpad.yaml
         - group_vars/jvb.yaml
         - group_vars/nodepool-launcher.yaml
-        - group_vars/refstack-docker.yaml
+        - group_vars/refstack.yaml
         - group_vars/registry.yaml
         - group_vars/review.yaml
         - group_vars/control-plane-clouds.yaml