CMS - make cross-section script configurable for year and test with 2016

[katilp]

Adapt utils/update_fixtures_cross_sections.py to be configurable and test it for 2016 datasets.

The 2016 cross-section values are available in https://cernbox.cern.ch/files/link/public/EHpyrdJet939vGy
and the records are temporarily in
eos ls /eos/opendata/cms/upload/kati

There will be some updates for records
69625
69627
69629
69631
69633
69635
69637
72704
72706
72714
72716
72756
72758
75595
75597
so do not update yet those *-part_*.json files where these record are.

They are in
cms-simulated-datasets-2016-part_70.json
cms-simulated-datasets-2016-part_71.json
cms-simulated-datasets-2016-part_81.json

[katilp]

Check that all processes that have values get included, i.e. all subdirs under MC2016/HiggsPhysics and MC2016/StandardModelPhysics. It does not appear for https://opendata-qa.cern.ch/record/75601
while that dataset has computed values under MC2016/StandardModelPhysics/ElectroWeak

Check also if we filtered out values with 0 for the line

"If this sample was generated at NLO, it has 0.000e+00% events with negative weights."

for 2015 values values. I think we did so as the text does not appear in the 2015 json files.

It would make sense to add it to the records only if the value differs from 0.