Fix: Expose HTTP errors when pulling layers

[jsoverson]

I just ran into an issue exacerbated by a load balancer where the initial pull would succeed, but subsequent layer pulls would fail and return 0-bytes for random layers.

Turns out that using request.byte_stream() (or request.bytes()) will succeed regardless of HTTP status, so error responses would still "succeed" with no data returned.

This PR turns non-success responses into errors.

[flavio]

Thanks for the fix, the CI error is completely unrelated, I'll fix it with another PR