Add ensure-tox to k8s and openshift jobs

We use tox to run the tests. Previously we were getting the
pre-installed tox from the opendev images. With the new images,
it's not there, so we need to run ensure-tox in our jobs.

Depends-On: https://review.opendev.org/735905
Change-Id: Ic1291eec079fbbd34ad69cf291f59219ed43e7d9

playbooks/nodepool-functional-k8s/pre.yaml

@@ -1,5 +1,6 @@
 - hosts: all
   roles:
     - role: bindep
+    - role: ensure-tox
     - role: ensure-kubernetes
       docker_version: 18.06.1~ce~3-0~ubuntu

playbooks/nodepool-functional-openshift/pre.yaml

@@ -12,6 +12,7 @@
 - hosts: launcher
   roles:
     - role: bindep
+    - role: ensure-tox
   tasks:
     - name: Ensure oc client is installed
       package: