Lists trials in the directory subtree starting at the given path.

def list_trials(experiment_path, sort, output, filter_op, columns,
                result_columns):
    """Lists trials in the directory subtree starting at the given path."""
    if columns:
        columns = columns.split(",")
    if result_columns:
        result_columns = result_columns.split(",")
    commands.list_trials(experiment_path, sort, output, filter_op, columns,
                         result_columns)