[BuildRules] use python3 in scripts

[smuzaffar]

many python tools are not available for python2 any more, so start using python3 for helpers scripts in cmssw-config

[smuzaffar]

please test

[cmsbuild]

A new Pull Request was created by @smuzaffar (Malik Shahzad Muzaffar) for branch IB/CMSSW_12_0_X/master.

@smuzaffar, @mrodozov, @iarspider can you please review it and eventually sign? Thanks.
@silviodonato, @dpiparo, @qliphy you are the release manager for this.
cms-bot commands are listed here

[smuzaffar]

test parameters:

• addpkg = FWCore,DataFormats

[smuzaffar]

please test

[smuzaffar]

lets get this in DEVEL IB

[cmsbuild]

+1

Summary: https://cmssdt.cern.ch/SDT/jenkins-artifacts/pull-request-integration/PR-ba2c22/15899/summary.html
COMMIT: ee88d35
CMSSW: CMSSW_12_0_X_2021-06-10-2300/slc7_amd64_gcc900
User test area: For local testing, you can use /cvmfs/cms-ci.cern.ch/week0/cms-sw/cmsdist/7015/15899/install.sh to create a dev area with all the needed externals and cmssw changes.

Comparison Summary

Summary:

• No significant changes to the logs found
• Reco comparison results: 0 differences found in the comparisons
• DQMHistoTests: Total files compared: 38
• DQMHistoTests: Total histograms compared: 2862520
• DQMHistoTests: Total failures: 1
• DQMHistoTests: Total nulls: 0
• DQMHistoTests: Total successes: 2862497
• DQMHistoTests: Total skipped: 22
• DQMHistoTests: Total Missing objects: 0
• DQMHistoSizes: Histogram memory added: 0.0 KiB( 37 files compared)
• Checked 160 log files, 37 edm output root files, 38 DQM output files
• TriggerResults: no differences found