MadGraphControl Fix, 21.6.43-patches branch (2020.11.02.)

See merge request !37826

So that the script would would with non-CVMFS-based installations as well.

Fixining conflicts in UserPhotonFlux from Pythia8.303

See merge request !36367

Fixing compatibility 8.303 (Nucleus2gamma2 conflicting with new  Nucleus2gamma class in PartonDistributions)

Updates to systematics tool in athena 21.6

See merge request !36324

fix wrong logic in unknownPDGIDTest

See merge request !36323

update to Pythia8.303

See merge request !36311

update to Pythia8.303 and go back to MG2.7.3

See merge request !36276

update to MG 2.8.0p3.atlas6

See merge request !36258

use the version patched for the m-range problem

See merge request !36174

update to MG 2.7.3p3.atlas6

See merge request !36133

Improving log dumping for MadGraphControl

See merge request !36131

It seems that sometimes the debug log file is not being properly
identified. Adding an extra catch to grab it in another set of
circumstances.

print sum of squared weights

See merge request !36081

comment out checks based on obsolete parameter inputconfcheck

See merge request !36061

change versions of Powheg and Pythia8

See merge request !35998

Add option to use powhegLHEReader for Herwig7 in Herwig72ConfigLHEF.py

See merge request !35962

Include systematics tool in athena 21.6

See merge request !35769

Update log file diff in post.sh

See merge request !35805

Prior to this change log file diffs in unit tests compared the reference file to the current
output, rather than the other way around, so that lines in the log removed due to local
changes are marked with a `+` in the diff output and lines added to the log are marked with
a `-`.

This commit switches the order of comparison with the aim of making the output more intuitive.
See discussion in ATEAM-644.

update to MG2.7.3

See merge request !35791