Network info model for nova

I'm tired of network_info being a list of tuples of dicts of lists of dicts that have to be looped through in many different places to get at certain pieces of information. As such I've created a somewhat generic model for storing the information compiled by nova network that the api and virt require. I've made it easy to pass through rpc and hydrate on the other side, and have built accessor functions for getting at specific information. This prevents code duplication of the looping mechanisms and abstracts the underlying structure from api and virt so every little change won't require refactoring across the board.