Make vertex collection configurable in class computing MVA for non-isolated electrons.

[matteosan1]

The MVA is now computed with the same vertex collection used in the electron producer (previously the collection name was hardcoded).
Additionally migrated one getByLabel to getByToken in the same class.
The change was esplicitly requested by HI people:
@yetkinyilmaz
@mandrenguyen
@istaslis

[cmsbuild]

A new Pull Request was created by @matteosan1 (Matteo Sani) for CMSSW_7_3_X.

Make vertex collection configurable in class computing MVA for non-isolated electrons.

It involves the following packages:

RecoEgamma/EgammaElectronProducers
RecoEgamma/ElectronIdentification

@cmsbuild, @nclopezo, @StoyanStoynev, @slava77 can you please review it and eventually sign? Thanks.
@lgray 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.
You can reject by replying to this message having '-1' in the first line of your reply.
@nclopezo 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: dcb36c3
https://cmssdt.cern.ch/SDT/jenkins-artifacts/pull-request-integration/PR-6374/861/summary.html

[cmsbuild]

Comparison is ready
https://cmssdt.cern.ch/SDT/jenkins-artifacts/pull-request-integration/PR-6374/861/summary.html

[slava77]

testing ... together with #6376

[slava77]

+1

for #6374 dcb36c3
tested in CMSSW_7_3_X_2014-11-13-1400 (test area sign461).
No changes in regular reco quantities as expected.

A summary of changes in HI is to appear in #6376

[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.