Prometheus: modify config to support k8s 1.6 by default (helm#1080)

* charts/stable/prometheus: modify config to support 1.6 by default

This commit adds support for Kubernetes 1.6 RBAC restrictions within
the prometheus configuration for scraping node metrics.

Fixes helm#955

Initial discussion of the issue:
prometheus/prometheus#2606

* stable/prometheus: bump chart minor version

stable/prometheus/Chart.yaml

@@ -1,5 +1,5 @@
 name: prometheus
-version: 3.0.3
+version: 3.1.0
 description: Prometheus is a monitoring system and time series database.
 home: https://prometheus.io/
 icon: https://raw.githubusercontent.com/prometheus/prometheus.github.io/master/assets/prometheus_logo-cb55bb5c346.png

stable/prometheus/values.yaml

@@ -515,6 +515,12 @@ serverFiles:
         relabel_configs:
           - action: labelmap
             regex: __meta_kubernetes_node_label_(.+)
+          - target_label: __address__
+            replacement: kubernetes.default.svc:443
+          - source_labels: [__meta_kubernetes_node_name]
+            regex: (.+)
+            target_label: __metrics_path__
+            replacement: /api/v1/nodes/${1}/proxy/metrics
 
       # Scrape config for service endpoints.
       #