stop using deprecated docker module in Ansible

[flavio-fernandes]

From the doc in Ansible site, it appears that the docker module being used in
roles/ovn is deprecated.
It should be changed to use docker_container and docker_image instead.

[huikang]

@flavio-fernandes if I understand correctly, the new docker_container and docker_image module requires

• ansible > 2.1.0
• docker-py >= 1.7.0
• Docker API >= 1.20

Considering the backward compatibility, I would prefer delaying the update a bit. But we should keep this in mind. What do you think?

[flavio-fernandes]

Make sense. docker module still works, so I would defer working on this until the time is right.