roles/mongodb: Add MongoDB deployment

The *mongodb* role installs MongoDB from the *mongodb.org* Yum
repository and manages basic server configuration.

roles/mongodb/tasks/main.yml

@@ -0,0 +1,18 @@
+- name: ensure mongodb package repository is available
+  template:
+    src=mongodb.repo.j2
+    dest=/etc/yum.repos.d/mongodb.repo
+    mode=0644
+  tags:
+  - install
+- name: ensure mongodb is installed
+  package:
+    name: mongodb-org-server
+    state: present
+  tags:
+  - install
+
+- name: ensure mongodb server starts at boot
+  service:
+    name=mongod
+    enabled=yes