CI: Force ansible to version 5

Default ansible version was changed in CI; this change is to validate
and workaround the issue by forcing the older ansible version. We will
still need to update the version before Zuul support for 5 is removed.

Change-Id: I3119055467a4edfdb13c522ce1c81d2f7eb3588d

.zuul.yaml

@@ -6,6 +6,7 @@
     nodeset: openstack-single-node-focal
     post-run: playbooks/integration/post.yaml
     run: playbooks/integration/run.yaml
+    ansible-version: 5
     irrelevant-files:
       - ^.*\.rst$
       - ^api-ref/.*$