Update docker tutorial

 * Use the standard installation instruction instead of the master
   version: 0.7 has been out for some time now.
 * As a result, switch to `sudo docker` instead of `sudo ./docker`.
 * Publish ports when running buildbot to be able to log into ssh and
   see the buildbot frontend.
 * Reformat the text
I would  say docker 1.0 or later. The [1.0 release post](http://blog.docker.com/2014/06/its-here-docker-1-0/) says:
> This release’s “1.0” label signifies a level of quality, feature completeness, backward compatibility and API stability to meet enterprise IT standards.

There are no details, but since we're not using advanced stuff, we should be good. (I don't know since when `--publish-all` is needed, but probably before 1.0.)