[WIP] AWS VPC module improvements

I started wrapping the boto VPC API and realized that I have no idea what should be exposed and what shouldn't.
I'd like that you guys and @colinbjohnson to review this PR and https://boto.readthedocs.org/en/latest/ref/vpc.html and tell me what should I expose.
This module is not tested at all. Can you guys provide instructions on how to test this?
Should I be using moto? Does salt have an AWS environment where the integration tests can run?
You're right. I also forgot to add that validation in all other exists methods.