Improve aiohttp usage for ddi (readchunk and timeout)
Improve aiohttp usage for ddi (readchunk and timeout)

Replaces read(chunk_size) with readchunk which reads as much as it can.
This is the better approach than to choose a chunk_size that works well
under all circumstances (HTTP, HTTPS).

Also, sets the timeouts properly. Before the context helper didn't do
anything since the requests would timeout after 5 minutes anyway.
Now, the timeouts are respected as expected.

Signed-off-by: Livio Bieri <db82c91311ba2b85d4265c083a7e6d329a9daff6@livio.li>

rauc/rauc-hawkbit