Use the new auth schema for Grafana

https://github.com/Mirantis/mk-lab-salt-model/pull/188
diff --git a/grafana/server/single.yml b/grafana/server/single.yml
index 911f32f..fd8f020 100644
--- a/grafana/server/single.yml
+++ b/grafana/server/single.yml
@@ -26,7 +26,8 @@
         user: grafana
         password: ${_param:mysql_grafana_password}
       auth:
-        engine: basic
+        basic:
+          enabled: true
       admin:
         user: ${_param:grafana_user}
         password: ${_param:grafana_password}