Add an use a utility service for gerrit commands

We have a need to run ad-hoc commands with the various things
mounted, such as the gerrit init, as well as our friends like
manage-projects. Make a second "service" that doesn't do anything,
but allows us to run "docker-compose run".

Change-Id: Ic9bafe85b90af413c891b969273437be9df6a79f

playbooks/roles/gerrit/tasks/start.yaml

@@ -1,14 +1,10 @@
-# TODO(mordred) Make this suck less, like if we could do an init container
-# or something just generally less gross.
 - name: Run gerrit init
+  shell:
+    cmd: >
+      docker-compose run shell
+      java -jar /var/gerrit/bin/gerrit.war init -d /var/gerrit -b --no-auto-start --install-all-plugins
+    chdir: /etc/gerrit-compose/
   when: gerrit_run_init | bool
-  command: >
-    docker run --rm --net=host -u gerrit
-    {% for volume in gerrit_container_volumes %}
-    -v {{ volume }}
-    {% endfor %}
-    {{ gerrit_container_image }}
-    /usr/local/openjdk-8/bin/java -jar /var/gerrit/bin/gerrit.war init -d /var/gerrit -b --no-auto-start --install-all-plugins
 
 - name: Run docker-compose up
   shell:

playbooks/roles/gerrit/templates/docker-compose.yaml.j2

@@ -8,4 +8,15 @@ services:
     volumes:
 {% for volume in gerrit_container_volumes %}
       - {{ volume }}
+{% endfor %}
+  # Utility "service" to allow us to run ad-hoc commands
+  shell:
+    image: {{ gerrit_container_image }}
+    restart: 'no'
+    command: /bin/true
+    network_mode: host
+    user: gerrit
+    volumes:
+{% for volume in gerrit_container_volumes %}
+      - {{ volume }}
 {% endfor %}