docker-admin is now a centos 7 container

The admin node has full functionality, but no care has been
taken to preserve backwards compatibility with a centos 6 based
admin node.

Part of that change was ditching using Apache for the provisioner
webserver in favor of a tiny static webserver in Go.

Another part was ditching the huge blob of stuff that is the omnibus packaged Chef Server + hacks to make it live on systemd in favor of an alternative chef-server implementation called goiardi

For testing and review, pls do not merge yet.