Fix container image publish to Docker Hub

Publishing container images to Docker Hub was failing with:

    state is present but all of the following are missing: source

This is caused by the recent Ansible upgrade by Zuul [1]: the source
parameter is mandatory since Ansible 2.12.

[1] https://review.opendev.org/c/openstack/project-config/+/849120

Change-Id: I232fe835f5a650c258243f1ee4720480f2e6e7b1
(cherry picked from commit 2da76f7)

tests/playbooks/publish.yml

@@ -21,6 +21,7 @@
           docker_image:
             name: "{{ item.RepoTags.0 }}"
             push: yes
+            source: local
           loop: "{{ docker_host_info.images }}"
       when: kolla_registry == 'dockerhub'