Added libvirt to Dockerfile

Signed-off-by: Cédric Bosdonnat <cedric.bosdonnat@free.fr>
Added libvirt-go to vendors

Signed-off-by: Cédric Bosdonnat <cedric.bosdonnat@free.fr>
Add pkg/rpcfd

This is a small unix-domain-sockets only wrapper around net/rpc
that adds support for passing file descriptors in rpc messages.

Docker-DCO-1.1-Signed-off-by: Alexander Larsson <alexl@redhat.com> (github: alexlarsson)
Docker-DCO-1.1-Signed-off-by: Josh Poimboeuf <jpoimboe@redhat.com> (github: jpoimboe)
pkg/cgroups: Export ParseCgroupFile

This is needed for the libvirt exec driver.
FIXME: replace this commit by a change in vendors.sh once it has been
approved in libcontainer

Docker-DCO-1.1-Signed-off-by: Alexander Larsson <alexl@redhat.com> (github: alexlarsson)
Docker-DCO-1.1-Signed-off-by: Josh Poimboeuf <jpoimboe@redhat.com> (github: jpoimboe)
Add .dockersocket directory to init layer

This will be used by the libvirt exec driver to mount in a directory
with the rpc socket, allowing the daemon to interact with the dockerinit

Docker-DCO-1.1-Signed-off-by: Alexander Larsson <alexl@redhat.com> (github: alexlarsson)
Docker-DCO-1.1-Signed-off-by: Josh Poimboeuf <jpoimboe@redhat.com> (github: jpoimboe)
add libvirt execdriver

Docker-DCO-1.1-Signed-off-by: Josh Poimboeuf <jpoimboe@redhat.com> (github: jpoimboe)
Docker-DCO-1.1-Signed-off-by: Alexander Larsson <alexl@redhat.com> (github: alexlarsson)
Signed-off-by: Cédric Bosdonnat <cedric.bosdonnat@free.fr>

Conflicts:
	Dockerfile
	Makefile
	hack/make.sh
	hack/make/binary
	hack/make/dynbinary
	runtime.go
	sysinit/sysinit.go
Add dockerinit tag to dynbinary builds

This excludes the libvirt execdriver go files depending on the libvirt
shared library when building dockerinit. Without this, ld can't find
-lvirt when building dockerinit... which will happen for all distros
not shipping the libvirt.a file.

Signed-off-by: Cédric Bosdonnat <cedric.bosdonnat@free.fr>
libvirt: pass env variables to dockerinit

Signed-off-by: Cédric Bosdonnat <cedric.bosdonnat@free.fr>