Ok, the main bugs have been fixed by the following socketserver fix.
commit b8f4163da30e16c7cd58fe04f4b17e38d53cd57e
Author: Victor Stinner <victor.stinner@gmail.com>
Date: Wed Sep 13 01:47:22 2017 -0700
bpo-31233: socketserver.ThreadingMixIn.server_close() (#3523)
socketserver.ThreadingMixIn now keeps a list of non-daemonic threads
to wait until all these threads complete in server_close().
Reenable test_logging skipped tests.
Fix SocketHandlerTest.tearDown(): close the socket handler before
stopping the server, so the server can join threads.
I'm not sure that it's possible to fix the bug in Python 3.6 without breaking the backward compatibility.
test_logging shouldn't fail with the threading_cleanup() warning anymore.