Upgrade Docker to 0.11 RC

* Default to installing from the Docker repository instead of Canonical repo
* Add ability to install from Docker repository, as Canonical repo lags
* Giver Docker non-root access
* Add docker alias when installed via docker.io package with update-alternatives
Adding box sizes to README.md
Merge remote-tracking branch 'upstream/master' into my

* upstream/master:
  Adding box sizes to README.md
  Upgrade Docker to 0.11 RC