Disable recursive git clone for ensure-devstack

This is not necessary, so disable it to avoid potential problems.

Change-Id: I34e05da59617e6a6666568bc50931a774ec51160

roles/ensure-devstack/tasks/main.yaml

@@ -11,6 +11,7 @@
     repo: https://opendev.org/openstack/devstack
     dest: /opt/devstack
     version: master
+    recursive: false
 - name: Write local.conf
   template:
     dest: /opt/devstack/local.conf