Allow to deploy several replicas of Grafana

Change-Id: I13ed33bd2b762dd5acee1de27103ac25b54a7a42
diff --git a/docker/swarm/service/dashboard/grafana_server.yml b/docker/swarm/service/dashboard/grafana_server.yml
index 5da0164..9da7aa5 100644
--- a/docker/swarm/service/dashboard/grafana_server.yml
+++ b/docker/swarm/service/dashboard/grafana_server.yml
@@ -1,5 +1,6 @@
 parameters:
   _param:
+    docker_grafana_replicas: 1
     grafana_database_type: sqlite3
     grafana_database_host: localhost
     grafana_database_port: 3306
@@ -8,7 +9,7 @@
     client:
       service:
         grafana_server:
-          replica: 1
+          replicas: ${_param:docker_grafana_replicas}
           environment:
             GF_DATABASE_TYPE: ${_param:grafana_database_type}
             GF_DATABASE_NAME: grafana