introduce NominalCollision2015 beamspot scenario, according to: https://indico.cern.ch/event/341218/; relvals as well as VtxSmearedDefaultKey not modified
Merge pull request #5578 from franzoni/beamspot_NominalCollision2015-CMSSW_7_3_X_2014-09-25-0200

introduce NominalCollision2015 beamspot scenario,