Add an integration test for roles

Add an app with roles to the integration tests. We'll deploy two web
containers and one worker. The worker just sleeps, so we are testing
that the container has booted.

test/integration/docker-compose.yml

@@ -62,3 +62,7 @@ services:
       context: docker/load_balancer
     ports:
       - "12345:80"
+    depends_on:
+      - vm1
+      - vm2
+      - vm3