Add Dismount-VHD driver method for hyper-v
Add Dismount-VHD driver method for hyper-v

chrisroberts/vagrant,mitchellh/vagrant,sni/vagrant,marxarelli/vagrant,chrisroberts/vagrant,mitchellh/vagrant,sni/vagrant,marxarelli/vagrant,mitchellh/vagrant,chrisroberts/vagrant,chrisroberts/vagrant,sni/vagrant,mitchellh/vagrant,marxarelli/vagrant,sni/vagrant,marxarelli/vagrant