This PR is dependent on the 2.1.0 release of the vagrant_cloud
library. It updates the `cloud` command to use the new interface
for interacting with the Vagrant Cloud API. It also adds support
for direct to backend storage uploads, and defaults to this
method.
Also included is a bit of cleanup refactoring, addition of method
documentation, and fixing up some small issues around custom username
usage within the internal client for authentication.
