parse testcase file and return locustfile path.
        if file_path is a Python file, assume it is a locustfile
        if file_path is a YAML/JSON file, convert it to locustfile

def parse_locustfile(file_path):
    """ parse testcase file and return locustfile path.
        if file_path is a Python file, assume it is a locustfile
        if file_path is a YAML/JSON file, convert it to locustfile
    """
    if not os.path.isfile(file_path):
        color_print("file path invalid, exit.", "RED")
        sys.exit(1)

    file_suffix = os.path.splitext(file_path)[1]
    if file_suffix == ".py":
        locustfile_path = file_path
    elif file_suffix in ['.yaml', '.yml', '.json']:
        locustfile_path = gen_locustfile(file_path)
    else:
        # '' or other suffix
        color_print("file type should be YAML/JSON/Python, exit.", "RED")
        sys.exit(1)

    return locustfile_path