Use conditions V2 by default

This pull request updates the default conditions DB to V2 by merging pull request 5541 from Andreas Pfeiffer.
It also removes the workaround for conditions DB V1 we were using because of a bug in ROOT 6 that has since been fixed.
This pull request fixes relval test failures.
Please merge as soon as convenient.
Once this is merged, file FWCore/Framework/data/cond_dump.root can be removed from the data area.