For Review: Driver for using Boot2Docker in Hyper-V on Windows

Do not merge, for review only.
This will not work without the Docker client supporting Windows, which is not merged yet:
https://github.com/docker/docker/pull/9113
https://github.com/Azure/docker/tree/windows-client
To test, merge Azure:windows-client with this MSOpenTech:hosts-hyperv branch.
You'll also need a boot2docker.iso newer than 1.3.1 with hyper-v support. This has been merged (https://github.com/boot2docker/boot2docker/pull/595)

This driver allows you to use boot2docker with Hyper-V, similar to the existing virtualbox driver

I added a `boot2docker-location` cli option, for specifying a local iso. I can add this to virtualbox too, if we want, or figure out how to merge `-location` with `-url`

Also, it would be good to figure out how to merge the common b2d options between virtualbox and hyper-v. And similarly, move the common code together (iso download, etc.). I'll start looking at this, but any ideas appreciated.