Fix more instances of "dotcloud/docker" in hack/ (and add a DOCKER_PKG environment variable to simplify references to our "package path" in our bundlescripts)

Docker-DCO-1.1-Signed-off-by: Andrew Page <admwiggin@gmail.com> (github: tianon)
Merge pull request #7338 from tianon/moar-dotcloud

Fix more instances of "dotcloud/docker" in hack/