Gen relval cmssw 7 2 0 pre7

- explicit DQMIO in datatier of GEN relvals
- fixes are intended to properly trigger the harvesting in production and documented also here https://hypernews.cern.ch/HyperNews/CMS/get/dataopsrequests/5638/1/1/2/1/1/1/1/1.html 

@bendavid 
@inugent