minimal Validation/RecoTrack/python/plotting/plotting.py fix for division changes in py3

[dan131riley]

PR description:

While making MTV plots comparing multiple scenarios, hit a problem with floating point array indices. This PR provides a minimal fix which allows plotting to proceed. There are probably more cases like this, I did not audit the code for other examples.

PR validation:

Prior to this PR, makeTrackValidationPlots.py --extended of multiple DQM outputs to compare would fail with an error about floating point array indices. With this PR, the same command succeeds.

[cmsbuild]

+code-checks

Logs: https://cmssdt.cern.ch/SDT/code-checks/cms-sw-PR-34708/24342

• This PR adds an extra 36KB to repository

[cmsbuild]

A new Pull Request was created by @dan131riley (Dan Riley) for master.

It involves the following packages:

• Validation/RecoTrack (dqm)

@andrius-k, @kmaeshima, @ErnestaP, @ahmad3213, @cmsbuild, @jfernan2, @rvenditti can you please review it and eventually sign? Thanks.
@felicepantaleo, @GiacomoSguazzoni, @JanFSchulte, @rovere, @VinInn, @ebrondol, @wmtford, @mmusich, @mtosi, @dgulhan this is something you requested to watch as well.
@silviodonato, @dpiparo, @qliphy, @perrotta you are the release manager for this.

cms-bot commands are listed here

[dan131riley]

Follow up to #34420, @makortel @davidlange6

[jfernan2]

please test

[cmsbuild]

+1

Summary: https://cmssdt.cern.ch/SDT/jenkins-artifacts/pull-request-integration/PR-056b1b/17376/summary.html
COMMIT: 20b8fab
CMSSW: CMSSW_12_1_X_2021-07-30-0900/slc7_amd64_gcc900
User test area: For local testing, you can use /cvmfs/cms-ci.cern.ch/week1/cms-sw/cmssw/34708/17376/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: 2 differences found in the comparisons
• DQMHistoTests: Total files compared: 39
• DQMHistoTests: Total histograms compared: 2998564
• DQMHistoTests: Total failures: 7
• DQMHistoTests: Total nulls: 0
• DQMHistoTests: Total successes: 2998535
• DQMHistoTests: Total skipped: 22
• DQMHistoTests: Total Missing objects: 0
• DQMHistoSizes: Histogram memory added: 0.0 KiB( 38 files compared)
• Checked 165 log files, 37 edm output root files, 39 DQM output files
• TriggerResults: no differences found

[jfernan2]

+1

[cmsbuild]

This pull request is fully signed and it will be integrated in one of the next master IBs (tests are also fine). This pull request will now be reviewed by the release team before it's merged. @silviodonato, @dpiparo, @qliphy, @perrotta (and backports should be raised in the release meeting by the corresponding L2)

[qliphy]

+1