migrate to appliance-tools

This moves the centos docker image build workflow in line with that of Fedora, my hope is to continue to update this as the Fedora workflow iterates.

For reference:
https://github.com/lsm5/docker-brew-fedora
https://github.com/lsm5/stackbrew/blob/master/library/fedora
https://index.docker.io/_/fedora/
https://fedoraproject.org/wiki/Changes/Docker_Container_Image