add install for prometheus node exporter

roles/prometheus-node-exporter/tasks/main.yml

@@ -0,0 +1,17 @@
+---
+- name: Install Prometheus Node exporter
+  apt:
+    name:
+      - prometheus-node-exporter
+    state: latest
+    update_cache: true
+  register: apt_result
+  retries: 3
+  until: apt_result is succeeded
+
+# TODO: add auth
+#
+# Create the file --web.config=/etc/node_exporter/config.yaml
+# and add --web.config=/etc/node_exporter/config.yaml to 
+# the args in /etc/default/prometheus-node-exporter
+#