Improve reporting of errors for image upload
By design Frisbee is independent of Emulab and its DB except for a narrow "configuration" API that allows them to interact, largely to obtain file names and do authentication. Unfortunately, there are no status reporting mechanisms, so Emulab utilities pretty much have to rely on the client or use server-side side-effects to determine if an image download or upload worked.
Upload is particularly a concern because there are a couple of server-side cases (over quota, upload limit hit) where the client cannot detect the problem because it is streaming from
imagezip and doesn't know how big the image is.