output_action (str): How the output is to be organized. Currently supported values are 'append_row' and 'summary_only'. 'append_row' - All values output by run() method invocations will be aggregated into one unique file named parallel_run_step.txt that is created in the output location. 'summary_only' Reference: https://docs.microsoft.com/en-us/python/api/azureml-contrib-pipeline-steps/azureml.contrib.pipeline.steps.parallelrunconfig