don't try to lock if using a specified tarball

The lock/subsys/lxc-ubuntu-cloud lock is to protect the tarballs
managed under /var/cache/lxc/cloud-$release.  Don't lock if we've
been handed a tarball.

fake device creation

Unprivileged users can't create devices, so bind mount null, tty, urandom
and console from the host.

Changelog:
	Jul 22: as Stéphane points out, remove a left-over debug line
Signed-off-by: Serge Hallyn <serge.hallyn@ubuntu.com>
Acked-by: Stéphane Graber <stgraber@ubuntu.com>