TLS 1.3 behaves slightly different than TLS 1.2. Session tickets and TLS
client cert auth are now handled after the initialy handshake. Tests now
either send/recv data to trigger session and client certs. Or tests
ignore ConnectionResetError / BrokenPipeError on the server side to
handle clients that force-close the socket fd.

To test TLS 1.3, OpenSSL 1.1.1-pre7-dev (git master + OpenSSL PR
https://github.com/openssl/openssl/pull/6340) is required.
Signed-off-by: Christian Heimes <christian@python.org>