Add puppet3 tests to xenial arm64

nb03.openstack.org still uses this, for now, so we should test
installation.

Change-Id: I305e796160927b1fb9954126a6631df87f6527db

zuul.d/system-config-roles.yaml

@@ -30,8 +30,8 @@
           nodes:
             - base
 
-# NOTE(ianw): There's no need to run puppet tests on this node because
-# we have no control-plane xenial arm64 nodes.
+# NOTE(ianw): Run puppet3 tests until nb03.openstack.org is gone
+# and we have no more puppet
 - job:
     name: system-config-zuul-role-integration-xenial-arm64
     parent: system-config-zuul-role-integration
@@ -40,6 +40,9 @@
         - name: base
           label: ubuntu-xenial
       groups:
+        - name: puppet3
+          nodes:
+            - base
         - name: openafs
           nodes:
             - base