package/utils: Prevent content automatic deflate in download function

The python requests library automatically deflate downloaded content bytes
if the response header content-encoding is set to a supported encoding.

However some HTTP servers can serve a tarball with content-type set to
application/x-gzip and content-encoding set to gzip which is wrong as
tarball is uncompressed while downloading it.

That behavior can make a file checksum check after download fail as the
expected checksum was computed on the compressed version of the file, not
the uncompressed one.

So ensure to prevent automatic deflate by reading response raw content
instead of using the iter_content method when the content-type and
content-encoding headers are both set to gzip format.