'When the process for the results directory is executed, the given file
contents will be placed in a file on the drone.  Returns the path at
which the file will be placed.'

def attach_file_to_execution(self, results_dir, file_contents, file_path=None):

    if (not file_path):
        file_path = self.get_temporary_path('attach')
    files_for_execution = self._attached_files.setdefault(results_dir, {})
    assert (file_path not in files_for_execution)
    files_for_execution[file_path] = file_contents
    return file_path
