surface artifact retreval failures in a build

[Andy Whitcroft]

When a build completes succussfully but we are unable to retrieve the build artifacts say due to a network error we end up with a failed job with no log information to indicate the cause of the issue. Could we perhaps record the underlying failure in either a new log (the download log) or consider that as part of the upload and reuse that log (as we cannot have a failed download and upload successful or otherwise on the same build).