Fix failed migration handling 8382

[cmsdmwmbot]

Jenkins results:

• Python3 Pylint check: failed
  • 9 warnings and errors that must be fixed
  • 1 warnings
  • 32 comments to review
• Pycodestyle check: succeeded
  • 49 comments to review

Details at https://cmssdt.cern.ch/dmwm-jenkins/view/All/job/DMWM-CRABServer-PR-test/1975/artifact/artifacts/PullRequestReport.html

[belforte]

will merge this with the fix for failed migrations. And open a new one for PublishMaster pylint and cleanup