Release flocker 0.2.1 - 847

Ok. Here's another build. This time with updated what's new version number.

 * Docs: https://docs.clusterhq.com/en/0.2.1/
 * Wheel: https://storage.googleapis.com/archive.clusterhq.com/downloads/flocker/Flocker-0.2.1-py2-none-any.whl
 * Sdist: https://storage.googleapis.com/archive.clusterhq.com/downloads/flocker/Flocker-0.2.1.tar.gz
 * Tutorial Base Box: https://storage.googleapis.com/clusterhq-vagrant/flocker-tutorial-0.2.1.box
 * Vagrant Cloud: https://vagrantcloud.com/clusterhq/boxes/flocker-tutorial/versions/4

The corresponding HomeBrew branch needs reviewing and testing too:
 * HomeBrew: https://github.com/ClusterHQ/homebrew-tap/pull/10

`brew install https://raw.githubusercontent.com/ClusterHQ/homebrew-tap/release/flocker-${VERSION}/flocker.rb`

Fixes #847