Parse arguments.

def parse_arguments():
    """Parse arguments."""
    parser = create_parser()
    args = parser.parse_args()
    if not args.role_requirements_old_commit:
        args.role_requirements_old_commit = args.role_requirements
    if not args.rpc_product_old_commit:
        args.rpc_product_old_commit = args.rpc_product
    return args