Allow to deploy several replicas of Grafana

Change-Id: I13ed33bd2b762dd5acee1de27103ac25b54a7a42
diff --git a/docker/swarm/stack/dashboard.yml b/docker/swarm/stack/dashboard.yml
index e7667a2..2ee123b 100644
--- a/docker/swarm/stack/dashboard.yml
+++ b/docker/swarm/stack/dashboard.yml
@@ -1,5 +1,6 @@
 parameters:
   _param:
+    docker_grafana_replicas: 1
     grafana_database_type: sqlite3
     grafana_database_host: localhost
     grafana_database_port: 3306
@@ -11,7 +12,7 @@
           service:
             grafana:
               deploy:
-                replicas: 1
+                replicas: ${_param:docker_grafana_replicas}
                 restart_policy:
                   condition: any
               image: ${_param:docker_image_grafana}