update tlsfuzzer with TLS 1.3

This updates tlsfuzzer to the latest git master and enables the new TLS 1.3 tests.

I still disable "interleave" tests in test-tls13-zero-length-data.py as GnuTLS doesn't support interleaved data during handshake.

Fixes #411 (closed).

Reviewer's checklist:

• Any issues marked for closing are addressed
• There is a test suite reasonably covering new functionality or modifications
• Function naming, parameters, return values, types, etc., are consistent and according to CONTRIBUTION.md
• This feature/change has adequate documentation added
• No obvious mistakes in the code