Fastsim: 74X premixing: activate branches in MixingModule

[lveldere]

backport of #8608

rebasing after #8901 gets merged,
will remove the changes to the DataMixer from this pr.

[lveldere]

please test

[cmsbuild]

The tests are being triggered in jenkins.

[cmsbuild]

A new Pull Request was created by @lveldere for CMSSW_7_4_X.

Fastsim: 74X premixing: activate branches in MixingModule

It involves the following packages:

SimGeneral/DataMixingModule
SimGeneral/MixingModule

@cmsbuild, @civanch, @nclopezo, @mdhildreth can you please review it and eventually sign? Thanks.
@wmtan this is something you requested to watch as well.
You can sign-off by replying to this message having '+1' in the first line of your reply.
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If you are a L2 or a release manager you can ask for tests by saying 'please test' in the first line of a comment.
@Degano you are the release manager for this.
You can merge this pull request by typing 'merge' in the first line of your comment.

[cmsbuild]

+1
Tested at: fa03ffb
https://cmssdt.cern.ch/SDT/jenkins-artifacts/pull-request-integration/PR-8902/4429/summary.html

[lveldere]

closing this until decided how/when to backport exactly

[cmsbuild]

+1
Tested at: fa03ffb
https://cmssdt.cern.ch/SDT/jenkins-artifacts/pull-request-integration/PR-8902/4445/summary.html

[cmsbuild]

Comparison is ready
https://cmssdt.cern.ch/SDT/jenkins-artifacts/pull-request-integration/PR-8902/4445/summary.html

The workflows 140.53 have different files in step1_dasquery.log than the ones found in the baseline. You may want to check and retrigger the tests if necessary. You can check it in the "files" directory in the results of the comparisons