Remove use of ROOT global gRandom

[dan131riley]

nbPileupEvents.seed used the global ROOT gRandom, which is not thread safe and breaks replay. This patch adds a local version of the ROOT GetRandom histogram function using the CMS standard HepRandomEngine instead. It also fixes a small logic error in the histogram normalization checks.

[cmsbuild]

A new Pull Request was created by @dan131riley (Dan Riley) for CMSSW_7_6_X.

Remove use of ROOT global gRandom

It involves the following packages:

Mixing/Base
SimGeneral/MixingModule

@cmsbuild, @civanch, @mdhildreth can you please review it and eventually sign? Thanks.
@wmtan this is something you requested to watch as well.
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[Dr15Jones]

please test

[cmsbuild]

The tests are being triggered in jenkins.

[cmsbuild]

+1
Tested at: 135db53
https://cmssdt.cern.ch/SDT/jenkins-artifacts/pull-request-integration/PR-11422/8265/summary.html

[cmsbuild]

Comparison is ready
https://cmssdt.cern.ch/SDT/jenkins-artifacts/pull-request-integration/PR-11422/8265/summary.html

[civanch]

+1

[cmsbuild]

This pull request is fully signed and it will be integrated in one of the next CMSSW_7_6_X IBs (tests are also fine). This pull request requires discussion in the ORP meeting before it's merged. @davidlange6, @Degano, @smuzaffar

[davidlange6]

+1