The lxc-debian is epurated and consolidated with a better
error handling.

This script is no longer interactive but it installs in a specified
place the debian rootfs.

This script is not supposed to be called directly so it will fall in
libexec path very soon. This script is called by lxc-create
as a template with the right option and the right place.

The debian network configuration is by dhcp.
Signed-off-by: Daniel Lezcano <dlezcano@fr.ibm.com>