Fix one more CondCore unit test

[mmusich]

Resolves #29983

PR description:

Addresses issue raised at #29983 (comment).
I profit of this PR (in commit 8612e67) also to fix the test CondCore/Utilities/test/testPngHistograms.cpp which was actually not doing anything useful.

PR validation:

Relies on the existing unit tests, both in CMSSW_11_2_X_2020-05-27-2300 and CMSSW_11_2_PY3_X_2020-05-27-2300

if this PR is a backport please specify the original PR and why you need to backport that PR:

Not a backport, and no backport are needed.

[mmusich]

type bug-fix

[cmsbuild]

The code-checks are being triggered in jenkins.

[mmusich]

@cmsbuild, please test for CMSSW_11_2_PY3_X

[cmsbuild]

+code-checks

Logs: https://cmssdt.cern.ch/SDT/code-checks/cms-sw-PR-30008/15698

• This PR adds an extra 12KB to repository

[cmsbuild]

The tests are being triggered in jenkins.
Test Parameters:

• RELEASE_FORMAT = CMSSW_11_2_PY3_X
  https://cmssdt.cern.ch/jenkins/job/ib-run-pr-tests/6641/console Started: 2020/05/28 11:41

[cmsbuild]

A new Pull Request was created by @mmusich (Marco Musich) for master.

It involves the following packages:

CondCore/Utilities

@ggovi, @cmsbuild can you please review it and eventually sign? Thanks.
@mmusich this is something you requested to watch as well.
@silviodonato, @dpiparo you are the release manager for this.

cms-bot commands are listed here

[cmsbuild]

+1
Tested at: 8612e67
https://cmssdt.cern.ch/SDT/jenkins-artifacts/pull-request-integration/PR-3d201f/6641/summary.html
CMSSW: CMSSW_11_2_PY3_X_2020-05-27-2300
SCRAM_ARCH: slc7_amd64_gcc820

[cmsbuild]

Comparison is ready
https://cmssdt.cern.ch/SDT/jenkins-artifacts/pull-request-integration/PR-3d201f/6641/summary.html

Comparison Summary:

• No significant changes to the logs found
• Reco comparison results: 4230 differences found in the comparisons
• DQMHistoTests: Total files compared: 36
• DQMHistoTests: Total histograms compared: 2782372
• DQMHistoTests: Total failures: 742
• DQMHistoTests: Total nulls: 0
• DQMHistoTests: Total successes: 2781630
• DQMHistoTests: Total skipped: 0
• DQMHistoTests: Total Missing objects: 0
• DQMHistoSizes: Histogram memory added: 0.0 KiB( 35 files compared)
• Checked 152 log files, 16 edm output root files, 36 DQM output files

[silviodonato]

Do you have any comments? @ggovi

[ggovi]

+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 (and backports should be raised in the release meeting by the corresponding L2)

[silviodonato]

+1