[TLS13] Add client auth

[gpotter2]

• rebase of https://github.com/romain-perez/scapy/tree/add-tls13-client-auth
• PR finished
• unit tests added

[codecov]

Codecov Report

Merging #2585 into master will decrease coverage by 0.30%.
The diff coverage is 73.63%.

@@            Coverage Diff             @@
##           master    #2585      +/-   ##
==========================================
- Coverage   88.49%   88.18%   -0.31%     
==========================================
  Files         246      246              
  Lines       51895    52003     +108     
==========================================
- Hits        45922    45858      -64     
- Misses       5973     6145     +172     

Impacted Files	Coverage Δ
scapy/layers/tls/record.py	90.80% <0.00%> (+0.34%)	⬆️
scapy/layers/tls/automaton_cli.py	82.67% <62.16%> (-1.10%)	⬇️
scapy/layers/tls/automaton_srv.py	78.03% <76.36%> (-0.13%)	⬇️
scapy/automaton.py	88.00% <100.00%> (+0.13%)	⬆️
scapy/layers/tls/handshake.py	87.29% <100.00%> (+0.97%)	⬆️
scapy/layers/tls/keyexchange.py	81.79% <100.00%> (-0.21%)	⬇️
scapy/layers/tls/record_tls13.py	86.25% <100.00%> (+2.92%)	⬆️
scapy/contrib/automotive/obd/scanner.py	6.74% <0.00%> (-89.89%)	⬇️
scapy/contrib/cansocket.py	70.83% <0.00%> (-8.34%)	⬇️
scapy/contrib/isotp.py	85.98% <0.00%> (-5.58%)	⬇️
... and 22 more

[gpotter2]

Tests don't pass on travis because it uses OpenSSL 1.0.2g which doesn't support tls 1.3 (it needs OpenSSL 1.1.1).

I'll pin Ubuntu Bionic on travis

[gpotter2]

@guedou @p-l- Ready for review

[guedou]

Awesome PR! I made some comments, most are cosmetic.