updated run_workflow.py to handle the multiple runs being returned by get_subject better
updated run_workflow.py to handle the multiple runs being returned by get_subject better

shoshber/fmriprep,oesteban/preprocessing-workflow,oesteban/fmriprep,poldracklab/fmriprep,poldracklab/fmriprep,poldracklab/preprocessing-workflow,poldracklab/fmriprep,shoshber/fmriprep,oesteban/preprocessing-workflow,chrisfilo/fmriprep,oesteban/fmriprep,oesteban/fmriprep,poldracklab/preprocessing-workflow