I can't reproduce test_start_tls_server_1 fails when I do (screenshot attached)

1. run test_asyncio
2. run test_asyncio.test_sslproto
3. run test_asyncio.test_sslproto -m test_start_tls_server_1

I run them in Windows 7 VM on Mac OS.

All other tests pass fine for me except test_sendfile_close_peer_in_the_middle_of_receiving.  Andrew, please look at this, this is your test, and I'm not sure I follow why we use SNDBUF at all. IMO it should be possible to write a test without using that (or if not, maybe time to use mocks).

With regards to start_tls tests -- I give up, I don't have time to look into this before 3.7.0.  I suggest to mask the test on the specific win buildbot it crashes on and fix it before 3.7.1 (or maybe when Windows users come up with a reliable way to reproduce the bug).