This endpoint will serve as a proxy for the openstack/defcore
repository. Instead of the UI sending requests to GitHub directly
where requests might be impeded due to cross-origin blockage or API
rate-limiting, the UI will be able to send requests to the Refstack
API in order to get capability data. The requests-cache library is
used so as not to keep sending requests to GitHub when likely
nothing has changed. With this, Refstack no longer has to worry about
mirroring capability files and keeping them updated.
GET /v1/capabilities - list all capability files
GET /v1/capabilities/2015.03 - get contents of file 2015.03.json
Change-Id: I6d327273f191e3339219e35eed8768da35c5bffb
961e46df6c