libvirt users - Dec 2016 - how to create container image for an existing container

Dear all,

I installed 8 containers using "yum --installroot=/root/fedora16lxc"
to create the container filesystem. Now I want to manage these containers with
openstack. So I need to deploy these containers by openstack which needs the
container image.

Can anyone tell me how to export my existing container's image? I am not
sure if openstack can create container without an image file. And I don't
want to use Docker.

Thank you in advance.
Cheng