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

Mostly a rewrite to use the official mongodb packages so we can use 2.6.5.

Also have tidied up and automated (tho still needs work) the admin user creation, and normal user creation.

There are helpers for replica set creation, and reindexing, recovery.

So that we know that mongo is in a stopped state after this script has run - and then we can ensure that salt starts it via upstart.

This script should only ever be run on an unconfigured database, so its safe.