Implement libvirt/KVM support

This adds a new driver for machine supporting the libvirt
and KVM back-end.  At present, it assumes "default" libvirt
NAT networking using dnsmasq.

Dockerfile

@@ -1,11 +1,12 @@
 FROM golang:1.3-cross
-RUN apt-get update && apt-get install -y --no-install-recommends openssh-client
+RUN apt-get update && apt-get install -y --no-install-recommends openssh-client libvirt-dev
 
 # TODO: Vendor these `go get` commands using Godep.
 RUN go get github.com/mitchellh/gox
 RUN go get github.com/aktau/github-release
 RUN go get github.com/tools/godep
 RUN go get code.google.com/p/go.tools/cmd/cover
+RUN go get github.com/alexzorin/libvirt-go
 
 ENV GOPATH /go/src/github.com/docker/machine/Godeps/_workspace:/go
 ENV MACHINE_BINARY /go/src/github.com/docker/machine/docker-machine

commands.go

@@ -20,6 +20,7 @@ import (
 	_ "github.com/docker/machine/drivers/digitalocean"
 	_ "github.com/docker/machine/drivers/google"
 	_ "github.com/docker/machine/drivers/hyperv"
+	_ "github.com/docker/machine/drivers/libvirt"
 	_ "github.com/docker/machine/drivers/none"
 	_ "github.com/docker/machine/drivers/openstack"
 	_ "github.com/docker/machine/drivers/rackspace"

drivers/libvirt/libvirt.go

@@ -0,0 +1 @@
+package libvirt