Updated _format_arg to produce a n_iterations only output if convergence threshold is not specified in N4BiasField Correction. Tests updated to match (with updates for image_dimension changes).
Updated _format_arg to produce a n_iterations only output if convergence threshold is not specified in N4BiasField Correction. Tests updated to match (with updates for image_dimension changes).

blakedewey/nipype,sgiavasis/nipype,iglpdc/nipype,sgiavasis/nipype,FCP-INDI/nipype,wanderine/nipype,gerddie/nipype,sgiavasis/nipype,carolFrohlich/nipype,glatard/nipype,glatard/nipype,blakedewey/nipype,blakedewey/nipype,carolFrohlich/nipype,gerddie/nipype,sgiavasis/nipype,mick-d/nipype,blakedewey/nipype,FCP-INDI/nipype,glatard/nipype,mick-d/nipype,gerddie/nipype,FCP-INDI/nipype,mick-d/nipype,pearsonlab/nipype,wanderine/nipype,dgellis90/nipype,glatard/nipype,dgellis90/nipype,dgellis90/nipype,wanderine/nipype,carolFrohlich/nipype,pearsonlab/nipype,pearsonlab/nipype,gerddie/nipype,iglpdc/nipype,pearsonlab/nipype,mick-d/nipype,dgellis90/nipype,FCP-INDI/nipype,iglpdc/nipype,wanderine/nipype,iglpdc/nipype,carolFrohlich/nipype