debug-logs: Don't log download errors at Debug
debug-logs: Don't log download errors at Debug

Before, we logged at Debug because the code assumed that some downloads
would fail. However, a commit sometime ago modified the logic to only
attempt downloads that should succeed. Thus, there is no reason to hide
download errors from users.

kklin/quilt,kklin/quilt,kayousterhout/quilt,NetSys/quilt,kklin/quilt,kelda/kelda,LuiseV/quilt,kklin/kelda,quilt/quilt,ejj/quilt-dev,kklin/kelda,quilt/quilt,kayousterhout/quilt,kklin/quilt,kelda/kelda,kayousterhout/quilt,NetSys/quilt,ejj/quilt-dev,LuiseV/quilt,NetSys/quilt,kelda/kelda,kklin/kelda,ejj/quilt-dev,kklin/kelda,LuiseV/quilt,kayousterhout/quilt,ejj/quilt-dev,kelda/kelda,LuiseV/quilt,quilt/quilt,NetSys/quilt,LuiseV/quilt,quilt/quilt,NetSys/quilt