S3 extension does not work correctly with range requests to HawkBit artifacts

[zyga]

Using the latest milestone snapshot of hawkbit and the s3 extension from this repository results in extremely poor performance (down to it not really working) for byte-range requests.

Casual inspection seems to indicate that the API for artifacts is not well suited for this. This prevents the use of hawkbit with s3 and rauc adaptive updates.

[zyga]

I suspect #71 is also showing another aspect of this problem.