Install docker-compose from pypi

We want to use stop_grace_period to manage gerrit service stops. This
feature was added in docker-compose 1.10 but the distro provides 1.5.
Work around this by installing docker-compose from pypi.

This seems like a useful feature and we want to manage docker-compose
the same way globally so move docker-compose installation into the
install-docker role.

New docker-compose has slightly different output that we must check for
in the gitea start/stop machinery. We also need to check for different
container name formatting in our test cases. We should pause here and
consider if this has any upgrade implications for our existing services.

Change-Id: Ia8249a2b84a2ef167ee4ffd66d7a7e7cff8e21fb

playbooks/roles/zuul-preview/tasks/main.yaml

@@ -2,11 +2,6 @@
   synchronize:
     src: zuul-preview-docker/
     dest: /etc/zuul-preview-docker/
-- name: Install docker-compose
-  package:
-    name:
-      - docker-compose
-    state: present
 - name: Run docker-compose pull
   shell:
     cmd: docker-compose pull