a fix for SUB=TH1F::Sumw2 error in DQM/Physics package

[anorkus]

A fix needed for issue found in here : #6177
Adds a check if Sumw2 call was done before.
Before when running a workflow (4.6) where multiple runs were processed bookHistograms method was called one than once and it triggered a "Sum of squares of weights structure already created" error.

[cmsbuild]

A new Pull Request was created by @anorkus (Antanas Norkus) for CMSSW_7_3_X.

a fix for SUB=TH1F::Sumw2 error in DQM/Physics package

It involves the following packages:

DQM/Physics

@nclopezo, @danduggan, @rovere, @cmsbuild, @deguio, @ojeda can you please review it and eventually sign? Thanks.
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@nclopezo, @ktf you are the release manager for this.
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[cmsbuild]

+1
Tested at: dfa4b61
https://cmssdt.cern.ch/SDT/jenkins-artifacts/pull-request-integration/PR-6241/703/summary.html

[cmsbuild]

Comparison is ready
https://cmssdt.cern.ch/SDT/jenkins-artifacts/pull-request-integration/PR-6241/703/summary.html

[deguio]

+1

[cmsbuild]

This pull request is fully signed and it will be integrated in one of the next CMSSW_7_3_X IBs unless changes (tests are also fine). This pull request will be automatically merged.