Replace TMVA::Factory->SetInputTrees with TMVA::DataLoader

[cmsbuild]

backport of #15737

The change is needed for ROOT 6.07.00 and above, i.e. for forthcoming
ROOT 6.08. The new release introduces a new TVMA class:
TMVA::DataLoader.

Signed-off-by: David Abdurachmanov David.Abdurachmanov@cern.ch

[cmsbuild]

A new Pull Request was created by @cmsbuild for CMSSW_9_0_X.

It involves the following packages:

PhysicsTools/MVATrainer

@cmsbuild, @monttj, @davidlange6 can you please review it and eventually sign? Thanks.
@imarches, @acaudron, @JyothsnaKomaragiri, @mverzett, @ferencek, @pvmulder this is something you requested to watch as well.
@davidlange6, @smuzaffar you are the release manager for this.

cms-bot commands are listed here #13028

[smuzaffar]

please test with cms-sw/cmsdist#2768

[cmsbuild]

The tests are being triggered in jenkins.
Using externals from cms-sw/cmsdist#2768
https://cmssdt.cern.ch/jenkins/job/cmsdist-cmssw-test-pr/89/console
https://cmssdt.cern.ch/jenkins/job/cmsdist-cmssw-test-pr/90/console
https://cmssdt.cern.ch/jenkins/job/cmsdist-cmssw-test-pr/91/console

[cmsbuild]

-1

Tested at: 4a1b99c

The following merge commits were also included on top of IB + this PR after doing git cms-merge-topic:
27ddd59
You can see more details here:
https://cmssdt.cern.ch/SDT/jenkins-artifacts/pull-request-integration/PR-17185/91/git-log-recent-commits
https://cmssdt.cern.ch/SDT/jenkins-artifacts/pull-request-integration/PR-17185/91/git-merge-result

You can see the results of the tests here:
https://cmssdt.cern.ch/SDT/jenkins-artifacts/pull-request-integration/PR-17185/91/summary.html

I found follow errors while testing this PR

Failed tests: UnitTests

• Unit Tests:

I found errors in the following unit tests:

---> test TestFWCoreIntegrationStandalone had ERRORS
---> test runtestPythonAnalysis had ERRORS
---> test testRecoMETMETProducers had ERRORS

The following merge commits were also included on top of IB + this PR after doing git cms-merge-topic:
27ddd59
You can see more details here:
https://cmssdt.cern.ch/SDT/jenkins-artifacts/pull-request-integration/PR-17185/91/git-log-recent-commits
https://cmssdt.cern.ch/SDT/jenkins-artifacts/pull-request-integration/PR-17185/91/git-merge-result

[cmsbuild]

Comparison job queued.

[cmsbuild]

Comparison is ready
https://cmssdt.cern.ch/SDT/jenkins-artifacts/pull-request-integration/PR-17185/91/summary.html

[Dr15Jones]

This broke the unit test
https://cmssdt.cern.ch/SDT/cgi-bin/buildlogs/slc6_amd64_gcc620/CMSSW_9_0_X_2017-01-17-0800/unitTestLogs/PhysicsTools/PythonAnalysis