Documentation: OpenStack authentication v2/v3 endpoints

It is possible to connect to either v2 or v3 Keystone auth endpoints for Swift storage, however this is undocumented. [An example connecting to a v3 auth endpoint](https://developer.ibm.com/recipes/tutorials/use-pkgcloud-to-access-ibm-object-storage-for-bluemix-with-node-js/) reveals the undocumented options.
