cmsRun returns non-zero if caught unix signal

If any of the signals cmsRun catches (SIGINT and SIGUSR2) are caught, cmsRun now returns a non zero value. This was requested by data ops.
Backported from CMSSW_7_0_X.
Merge pull request #1814 from Dr15Jones/cmsRunReturnNonZeroOnSignalFor4_1_X

Framework fix -- cmsRun returns non-zero if caught unix signal