adding the ability to add admin and other users to mongodb through recip...

...e, readme updates, kitchen integration tests
adds
- user_management recipe, which will require auth on mongo config
- user resource
- user provider
- users attributes
- user_management integration tests
That would mean they couldn't ever -not- have admin, though, right? And I'd see some uses to that... maybe. Running the recipe after an install already happened an and admin exists