lxc is special in that we cannot create the master outside of the
container without opening the slave because we have nothing to provide to the
cmd. We have to open both then do the crazy setup on command right now instead of
passing the console path to lxc and telling it to open up that console. we save a couple of
openfiles in the native driver because we can do this.
Docker-DCO-1.1-Signed-off-by: Michael Crosby <michael@docker.com> (github: crosbymichael)