Improved format for edmSTreamStallGrapher.py output

Made it clearer when the stall begins and ends.
Merge pull request #3935 from Dr15Jones/improveFormatForEdmStreamStallGrapher

Framework -- Improved format for edmSTreamStallGrapher.py output
Merge remote branch 'origin/CMSSW_7_1_X' into CMSSW_7_0_X