fix(metrics): replaces . with _ in instance name

closes #5739

conf/defaults.ini

@@ -353,7 +353,7 @@ enabled           = true
 interval_seconds  = 60
 
 # Send internal Grafana metrics to graphite
-; [metrics.graphite]
+[metrics.graphite]
 ; address = localhost:2003
 ; prefix = prod.grafana.%(instance_name)s.
 

conf/sample.ini

@@ -297,15 +297,15 @@ check_for_updates = true
 # Metrics available at HTTP API Url /api/metrics
 [metrics]
 # Disable / Enable internal metrics
-;enabled           = true
+enabled           = true
 
 # Publish interval
 ;interval_seconds  = 10
 
-# Send internal metrics to Graphite
-; [metrics.graphite]
+# Send internal metrics to Graphite. %instance_name% in prefix will be replaced with the value of instance_name
+[metrics.graphite]
 ; address = localhost:2003
-; prefix = prod.grafana.%(instance_name)s.
+; prefix = service.grafana.%instance_name%
 
 #################################### Internal Grafana Metrics ##########################
 # Url used to to import dashboards directly from Grafana.net