Pythia 8.200pre2 (71x)

Backport of interface changes for pythia 8.2.
Needs to be merged together with 
https://github.com/cms-sw/cmsdist/pull/1065/
@bendavid 

Hi Josh

In #5602 you changed the way the pythia flags are set in this file.
Why not here in 71?

Cheers

Lukas