Configure Prometheus to scrape Kubelets directly

* Use Kubelet bearer token authn/authz to scrape metrics
* Drop RBAC permission from nodes/proxy to nodes/metrics
* Stop proxying kubelet scrapes through the apiserver, since
this required higher privilege (nodes/proxy) and can add
load to the apiserver on large clusters

addons/prometheus/rbac/cluster-role.yaml

@@ -6,7 +6,7 @@ rules:
 - apiGroups: [""]
   resources:
   - nodes
-  - nodes/proxy
+  - nodes/metrics
   - services
   - endpoints
   - pods