CondCore/CondDB: add missing <tuple> include

Signed-off-by: David Abdurachmanov <David.Abdurachmanov@cern.ch>
Merge pull request #2416 from davidlt/add-missing-tuple-include

CondCore/CondDB: add missing <tuple> include
Merge remote branch 'origin/CMSSW_7_1_X' into CMSSW_7_0_X