Update mixing scenario names (for 7_5_X)

[gsfs]

Identical to pull request #12545 for 8_0_X, here requested for 7_5_X which will be used for 2015 pp and PbPb data at 5 TeV
Fixed a typo in existing mixing scenario names to avoid future confusion.
Added new mixing scenario names for use with 5 TeV pp and PbPb

[cmsbuild]

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

It involves the following packages:

Configuration/StandardSequences

@cmsbuild, @franzoni, @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.
@slava77, @Degano, @smuzaffar you are the release manager for this.

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[slava77]

@cmsbuild please test

http://cern.ch/go/pw8P from 262325 pp ref run looks consistent with the choice of range here

[cmsbuild]

The tests are being triggered in jenkins.
https://cmssdt.cern.ch/jenkins/job/ib-any-integration/9902/console

[cmsbuild]

+1
Tested at: ab0ad25
https://cmssdt.cern.ch/SDT/jenkins-artifacts/pull-request-integration/PR-12547/9902/summary.html

[cmsbuild]

Comparison is ready
https://cmssdt.cern.ch/SDT/jenkins-artifacts/pull-request-integration/PR-12547/9902/summary.html

[slava77]

merge