master: LHEFilters updates for AthGeneration
requested to merge atlas-physics/pmg/mcexperts/powheg-experts/athena:master-Updating-LHEFilters into master
This MR adds a new LHE filter in MCJobOptionUtils, to select events with a certain number of final state quarks, possibly with a certain parent (e.g. to select Z->bb events among Z->jj).
I also did some modifications to make sure that the LHE filters works with python3.
NB: this makes the sweep from 21.6 of !53969 (merged) manually.