Extend tests vars overrides

This ensures that our group vars are well applied.
This check is useful to ensure the default inventory loads fine,
which would fail to apply group vars if it wasn't loading properly.

Change-Id: Idc1a2be1ee761ed01c3b54547fd3be804b0c0c33

tests/test-vars-overrides.yml

@@ -19,6 +19,10 @@
   connection: local
   user: root
   tasks:
+    - name: Ensuring existing group vars are well applied
+      assert:
+        that:
+          - "openstack_release is defined"
     - name: Ensuring babar is well defined
       assert:
         that: