First, run commands:
$ vagrant up
$ vagrant ssh
$ docker -v
Docker version 1.11.2, build b9f10c9
$ docker-compose -v
docker-compose version 1.7.0, build 0d7bf73
$ vagrant package --output ubuntu_docker.box
Then, upload ubuntu_docker.box
from this page: https://atlas.hashicorp.com/boxes/new.
It's available here: https://atlas.hashicorp.com/hiogawa/boxes/ubuntu_docker/