clean up test flirt function, have it use new support functions
clean up test flirt function, have it use new support functions

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