Provide pretty status bars to indicate upload progress for tasks that
perform large file uploads to the API ('provisioner ova upload' and
'storage volume upload') so the administrator can gauge progress and
estimated time to completion.
Move all API calls to a new common function called call_api to
facilitate easier future changes. Use this function to implement API key
handling via request header value as well as integrate the request URI
generation and debug output handling.
Closes#65
Joshua Boniface