roles/grafana: Deploy Grafana

This commit introduces the *grafana* role and the corresponding
`grafana.yml` playbook.  The role installs Grafana using the system
package manager, and configures the server (including LDAP
authentication).

roles/grafana/handlers/main.yml

@@ -0,0 +1,8 @@
+- name: restart grafana
+  service:
+    name: grafana-server
+    state: restarted
+- name: reload nginx
+  service:
+    name: nginx
+    state: reloaded