replaced runtime cms::Exception calls with edm::LogError calls
added default ghost rescaling factor
replacing repeating code blocks with function calls
Merge pull request #3787 from cms-btv-pog/JetFlavourLogError_from-CMSSW_6_2_X_SLHC_2014-05-09-1400

Replacing runtime cms::Exception calls with edm::LogError calls in the jet flavour code: Backport from 7_1_X to 6_2_X_SLHC