assure that no same GEN dataset can be over-written from different requests
all 6 workflows with root step 'DYToll01234Jets_5f_LO_MLM_Madgraph_LHE_13TeV' will recycle the same dataset, from wf [512] of generator set
Merge pull request #6692 from franzoni/gf-DScollision-GENrelvals-CMSSW_7_4_X

assure no DS collision LHE relvals