Switch one of the CI jobs to Python 3

Change-Id: Ib513a713ac95da9ed14ea24643b4ea5b951892ec

.zuul.yaml

@@ -125,12 +125,15 @@
       metalsmith_whole_disk_image: test-centos-wholedisk
 
 - job:
-    name: metalsmith-integration-glance-netboot-cirros-iscsi
+    name: metalsmith-integration-glance-netboot-cirros-iscsi-py3
     description: |
         Integration job using Glance as image source and CirrOS with netboot.
     parent: metalsmith-integration-base
     vars:
+      devstack_localrc:
+        USE_PYTHON3: true
       metalsmith_netboot: true
+      metalsmith_python: python3
 
 - job:
     name: metalsmith-integration-glance-netboot-cirros-direct
@@ -156,11 +159,11 @@
       jobs:
         - openstack-tox-lower-constraints
         - metalsmith-integration-glance-localboot-centos7
-        - metalsmith-integration-glance-netboot-cirros-iscsi
+        - metalsmith-integration-glance-netboot-cirros-iscsi-py3
         - metalsmith-integration-glance-netboot-cirros-direct
     gate:
       jobs:
         - openstack-tox-lower-constraints
         - metalsmith-integration-glance-localboot-centos7
-        - metalsmith-integration-glance-netboot-cirros-iscsi
+        - metalsmith-integration-glance-netboot-cirros-iscsi-py3
         - metalsmith-integration-glance-netboot-cirros-direct

playbooks/integration/pre.yaml

@@ -8,9 +8,13 @@
         name: -r /opt/stack/metalsmith/requirements.txt
         extra_args: -c /opt/stack/requirements/upper-constraints.txt
       become: true
+      vars:
+        ansible_python_interpreter: /usr/bin/{{ metalsmith_python | default('python') }}
 
     - name: Install metalsmith
       pip:
         name: /opt/stack/metalsmith
         editable: true
       become: true
+      vars:
+        ansible_python_interpreter: /usr/bin/{{ metalsmith_python | default('python') }}