The Dockerfile.j2 is deprecated, replaced by a common one, and the
molecule.yml "platform" section is optional, usually we can rely on the
default content.
This patch also introduces a new playbook dedicated for zuul, allowing
to prepare the env for the "role-addition" test env.
Change-Id: I9bfa945abeebed1e0c46c27732d6c4bb398a2538
698d8dea9a