Install pypy on the vagrant dev box.
Merge pull request #968 from ClusterHQ/pypy-dev-box

[FLOC-980] Install pypy on the vagrant dev box

Author: @tomprince 
Reviewer: @wallrj
Fixes https://clusterhq.atlassian.net/browse/FLOC-980
Fixes https://clusterhq.atlassian.net/browse/FLOC-588