The lxc-create command is now able to call a sub script to install
a mini template.
Right now, debian is supported.

The rootfs is stored automatically in <lxcpath>/<name>/rootfs
So the rootfs is a subdirectory of the container configuration directory.

When lxc-destroy is called, the rootfs is deleted with the container
configuration.
Signed-off-by: Daniel Lezcano <dlezcano@fr.ibm.com>