Strengthen myNumJobStarts in simple.sh

[shreyb]

In simple.sh, with PR #655, we added

    myNumJobStarts=$(awk -F "=" '/^NumJobStarts / {print int($2)}' ${_CONDOR_JOB_AD})

This could be more robust. If $_CONDOR_JOB_AD is not set the awk command will hang, waiting on stdin.

Originally posted by @retzkek in #655 (comment)