tox: add ceph_stable_release to switch2container

We need to set the ceph_stable_release variable during the switch2container
playbook.

Signed-off-by: Dimitri Savineau <dsavinea@redhat.com>

tox.ini

@@ -198,6 +198,7 @@ commands=
 commands=
   ansible-playbook -vv -i {changedir}/{env:INVENTORY} {toxinidir}/infrastructure-playbooks/switch-from-non-containerized-to-containerized-ceph-daemons.yml --extra-vars "\
       ireallymeanit=yes \
+      ceph_stable_release={env:CEPH_STABLE_RELEASE:octopus} \
       ceph_docker_registry_auth=True \
       ceph_docker_registry_username={env:DOCKER_HUB_USERNAME} \
       ceph_docker_registry_password={env:DOCKER_HUB_PASSWORD} \