Allow uploads to retry if there are curl errors

[grahampugh]

Sometimes a curl error could be caused by an upload failure (e.g. error 55). This currently raises an error and quits, but it could be handled by the retries so that there are multiple chances for it to succeed.

This seems to be cause if curl errors in line 502:

subprocess.check_output(curl_cmd)

This should be converted to a try statement. The specific exception is subprocess.CalledProcessError. See https://pastebin.com/wwZZQgGN for an example error.