Create an lxc-clone script to clone containers.  It should probably
be factored into helpers and then enhanced, in particular to convert
between LVM and non-LVM containers, create non-snapshot LVM clones,
support loopback devices, and, when stable enough, to use
overlayfs, btrfs, etc.

But this is a start.
Signed-off-by: Serge Hallyn <serge.hallyn@ubuntu.com>
Signed-off-by: Daniel Lezcano <dlezcano@fr.ibm.com>