Refactor mongodb definition 

Quite a bit of cleanup of the mongodb definition, including:
* cleaning up whitespace
* break definition parameters into multiple lines (so diffs are easier to read)
* check mongodb_type at the beginning of the definition, raising a full ArgumentException on error
* extract params and node attributesinto a new_resource object (to more closely model a lwrp)
* update chef used for test-kitchen (required to work with recent apt cookbooks)

I've made sure to verify this passes test-kitchen.