Python3: fix a bytes/str issue

test_curl_log_i18n_headers, introduced in
0b730e82b4bf63be1c3acd924a77a684a31db709, does not work with Python 3, because
Python 3, the headers must also be bytes,

Change-Id: I7baf737b3d9e2763a43eb593ca8ea733274a1107
Merge "Python3: fix a bytes/str issue"
Support Python 3

This patch fixes an issue similar to one fixed by
fa4ef4dc00e220ccbc0e171ee6d3ee898deab0a3 and adds the required trove
classifiers to setup.cfg.

Change-Id: Ia77e943612de9aea78128b142981e70665714e1b