Update HI vtx smearing according to new beta*.

[mandrenguyen]

The beam conditions expected for the PbPb run have been changed.
See Tiziano's slides from the WGM:
https://indico.cern.ch/event/442020/contribution/0/attachments/1148526/1647556/WGM241.pdf

This PR updates the beta*.
I also took the opportunity to shift the beamspot centroid to the current pp locations.
Last time around in 2011, the centroid stayed fairly close between pp and PbPb, so this should be a better assumption than the origin.

This new vertex smearing is not the default, so there will be no change in relval.
We propose to switch this to the default when we reevaluate the reco beamspot and update the GT in a PR to come shortly, once we can produce some samples with this vertex smearing.

A 76X PR was also made #11138

[cmsbuild]

A new Pull Request was created by @mandrenguyen for CMSSW_7_5_X.

Update HI vtx smearing according to new beta*.

It involves the following packages:

Configuration/StandardSequences
IOMC/EventVertexGenerators

@cmsbuild, @civanch, @franzoni, @mdhildreth, @davidlange6 can you please review it and eventually sign? Thanks.
@ghellwig, @makortel, @GiacomoSguazzoni, @rovere, @VinInn, @Martin-Grunewald, @cerati, @dgulhan this is something you requested to watch as well.
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[civanch]

please test

[civanch]

+1

[cmsbuild]

The tests are being triggered in jenkins.

[cmsbuild]

+1
Tested at: 6874dfc
https://cmssdt.cern.ch/SDT/jenkins-artifacts/pull-request-integration/PR-11141/7927/summary.html

[cmsbuild]

Comparison is ready
https://cmssdt.cern.ch/SDT/jenkins-artifacts/pull-request-integration/PR-11141/7927/summary.html

[mandrenguyen]

@davidlange6
Can we please merge this such that we can start the HI GEN-SIM production?