When uploading box file, check if the size is greater than
5GB. If the size is larger and the direct to storage option
is enabled, disable the option due to current 5GB restriction
on direct uploads.
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.
This commit introduces a new uploader class for uploading files and
splits up some commonly used functionality between it and the downloader
class into a curl helper library.
