addons: Update Prometheus to v2.1.0

* Change service discovery to relabel jobs to align with
rule expressions in upstream examples
* Use a separate service account for prometheus instead
of granting roles to the namespace's default
* Use a separate service account for node-exporter
* Update node-exporter and kube-state-metrics exporters

addons/prometheus/rbac/cluster-role-binding.yaml

@@ -8,5 +8,5 @@ roleRef:
   name: prometheus
 subjects:
 - kind: ServiceAccount
-  name: default
+  name: prometheus
   namespace: monitoring