Validation code for BTagging at HLT


Re-ope of PR #5387

It is a validation code for the b-tagging at HLT.
It was presented in the DQM meeting : https://indico.cern.ch/event/294162/ 

News:
- implemented comments by @deguio
- integration of the validation in the central validation sequence (added in hltValidation of HLTriggerOffline/Common)
- tested with "python whiteRabbit.py" #3 and #4 , with small changes:
    - I'm using TTbar, instead of SingleMu, in order to have few jets, needed for b-tagging.
    - I'm also using the HLT:FULL menu, as it always run b-tagging (if you think the code has to use HLT:GRun, I can change quickly the code).

- Although I propose to add the code in the central validation sequence, I'd like to maintain the code used for a private b-tag validation (config.ini, test.py, .....)