prometheus operator, metrics for k8s cluster

install using Helm:
- Prometheus Operator
- metrics for k8s cluster including: grafana dashboard, alertmanager, node exporters

base project:
https://github.com/coreos/prometheus-operator

the issue:
https://github.com/kubernetes-incubator/kubespray/issues/2042

Previous PR, raw ansible without Helm:
https://github.com/kubernetes-incubator/kubespray/pull/2499

roles/kubernetes-apps/metrics/tasks/main.yml

@@ -0,0 +1,17 @@
+---
+- name: Metrics | Make sure Helm is installed
+  command: "{{ bin_dir }}/helm version"
+
+- name: Metrics | Add coreos repo
+  command: "{{ bin_dir }}/helm repo add coreos https://s3-eu-west-1.amazonaws.com/coreos-charts/stable/"
+  run_once: true
+
+- name: Metrics | Install Prometheus Operator
+  command: "{{ bin_dir }}/helm upgrade --install prometheus-operator coreos/prometheus-operator --namespace {{ monitoring_namespace }}"
+  when: prometheus_operator_enabled
+  run_once: true
+
+- name: Metrics | Install K8s cluster metrics
+  command: "{{ bin_dir }}/helm upgrade --install kube-prometheus     coreos/kube-prometheus     --namespace {{ monitoring_namespace }}"
+  when: k8s_metrics_enabled
+  run_once: true