All of the IdentityInterface outputs were wrong since the output has the same name as the input, not 'output_file' as I thought.
All of the IdentityInterface outputs were wrong since the output
has the same name as the input, not 'output_file' as I thought.

Replace all to use utils.Function with a function that copies
the input file to the output.

NIF-au/volgenmodel-nipype,carlohamalainen/volgenmodel-nipype,NIF-au/volgenmodel-nipype,NIF-au/volgenmodel-nipype,carlohamalainen/volgenmodel-nipype,NIF-au/volgenmodel-nipype,carlohamalainen/volgenmodel-nipype,carlohamalainen/volgenmodel-nipype