Ensure command line arguments are passed through run_tests

[dhgutteridge]

A pretty trivial patch, relevant if a user is both setting $PYTHON and supplying command line arguments, as I've had occasion to do.

[codecov]

Codecov Report

Merging #3196 (3c84f95) into master (11832de) will increase coverage by 0.30%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master    #3196      +/-   ##
==========================================
+ Coverage   87.17%   87.47%   +0.30%     
==========================================
  Files         267      267              
  Lines       55816    55824       +8     
==========================================
+ Hits        48655    48834     +179     
+ Misses       7161     6990     -171     

Impacted Files	Coverage Δ
scapy/layers/sixlowpan.py	86.33% <0.00%> (-0.26%)	⬇️
scapy/layers/tls/automaton_cli.py	76.14% <0.00%> (-0.09%)	⬇️
scapy/layers/dot11.py	90.53% <0.00%> (+0.01%)	⬆️
scapy/pipetool.py	88.35% <0.00%> (+0.02%)	⬆️
scapy/layers/inet.py	70.96% <0.00%> (+0.15%)	⬆️
scapy/layers/ntp.py	84.86% <0.00%> (+0.27%)	⬆️
scapy/asn1/ber.py	83.69% <0.00%> (+0.27%)	⬆️
scapy/supersocket.py	75.22% <0.00%> (+0.30%)	⬆️
scapy/utils.py	79.00% <0.00%> (+0.30%)	⬆️
scapy/layers/ppp.py	96.65% <0.00%> (+0.33%)	⬆️
... and 20 more

[gpotter2]

Makes a lot of sense. Thanks for the PR