Add possibility to set replicas

  * Docker aptly public
  * Docker registry

Change-Id: I70787482db7bd5e4fcd0ebbf4a266e856c132098
diff --git a/docker/swarm/stack/docker.yml b/docker/swarm/stack/docker.yml
index 7f8c153..f861718 100644
--- a/docker/swarm/stack/docker.yml
+++ b/docker/swarm/stack/docker.yml
@@ -2,6 +2,7 @@
   _param:
     docker_image_registry: registry:2
     docker_image_visualizer: dockersamples/visualizer
+    docker_stack_registry_replicas: 3
   docker:
     client:
       stack:
@@ -11,7 +12,7 @@
               environment:
                 REGISTRY_HTTP_SECRET: ${_param:docker_registry_http_secret}
               deploy:
-                replicas: 3
+                replicas: ${_param:docker_stack_registry_replicas}
                 restart_policy:
                   condition: any
               image: ${_param:docker_image_registry}