Hyper-V support.

Adds Hyper-V KVP daemon. This is a user space program to
communicate key-value-pairs to the hypervisor, through the
hyper-v kernel drivers.

Primary usage is to get the IP of the vm from the hypervisor. Boot2docker is already building and including the hyper-v kernel modules which get loaded automatically if running within hyper-v. The daemon is benign if the modules are not loaded. The daemon is 43K.
Can we gate this on a `modprobe` check or similar like we do the VBox Guest Additions code? https://github.com/boot2docker/boot2docker/blob/15db9a9b86e2703dabda2b27f0e60883942bf728/rootfs/rootfs/etc/rc.d/automount-shares#L8

Is there a simple check like that to verify that we are in fact in Hyper-V?