parametrized docker compose image

Change-Id: Ie98c688337876a5875bd9aecb6f5181b539e687a
diff --git a/docker/client.yml b/docker/client.yml
index 4691ddb..df11493 100644
--- a/docker/client.yml
+++ b/docker/client.yml
@@ -1,10 +1,12 @@
 classes:
   - service.docker.client
 parameters:
+  _param:
+    docker_image_compose: docker/compose:1.8.0
   docker:
     client:
       enabled: true
       compose:
         source:
           engine: docker
-          image: "docker/compose:1.8.0"
+          image: ${_param:docker_image_compose}