Initial management of MongoDB Org package

Includes simple helper wrappers around common admin tasks:

* recover
* reindex
* replica set creation
do not manage client for now
sensu check
fix initiate_replica_set bug
add create_mongo_user helper
handle adding users
Handle migration from legacy 'use_packaged_version'

We have to handle that we're potentially going from one (packaged)
version of mongo to a version from Mongo's own repo.
Use backupninja to back up mongo if available
automatically reindex
README updated
Improve reindex script

* Create indexes using db owner. Admin user cannot create them
* ensure we only index master
* bugfixes (typos)
Safeguard for deployment on 12.04, use new packages on 14.04
Improve recovery docs
Improve docs
Rename helpers to be mongo_*

... in order to group them, and to aid use via shell expansion
explicitly include dependencies
Merge pull request #1 from ministryofjustice/rewrite_with_org_packages

New MongoDB formula, rewritten to use official packages and APT repo