Template the mongodb configuration file and replace whatever is automatically installed

[ansell]

The mongodb role doesn't currently manage or update the configuration file. It should be templated in ansible and the template should replace whatever is present on the server (including backups, which ansible is capable of automatically doing).

In particular, the configuration file regularly needs to reference somewhere on the /data/ partition using the dbPath variable in the /etc/mongod.conf file. This would be enabled by templating that file and replacing it whenever ansible is run.

[vjrj]

To install CAS-5 I created this new role with code commented from aws-cas5 playbook. This new mongo role includes some initial template: https://github.com/AtlasOfLivingAustralia/ala-install/blob/master/ansible/roles/mongodb-org/templates/mongod.yml

Probably we should minimize the number of mongo roles but I was trying not to break production things.