We were trying to be smart and use whatever the last part of
the container's rootfs path was.  However for block devices
that doesn't make much sense.  I.e. if lxc.rootfs = /dev/md-1,
chances are that /var/lib/lxc/c1/md-1 does not exist.

So always use the $lxcpath/$lxcname/rootfs, and if it does
not exist, try to create it.

With this, 'lxc-clone -s -o c1 -n c2' where c1 has an lvm backend
is fixed.  See https://bugs.launchpad.net/ubuntu/+source/lxc/+bug/1414771Signed-off-by: Serge Hallyn <serge.hallyn@ubuntu.com>
Acked-by: Stéphane Graber <stgraber@ubuntu.com>