Prepare the socket file for raylet and plasma.

        This method helps to prepare a socket file.
        1. Make the directory if the directory does not exist.
        2. If the socket file exists, raise exception.

        Args:
            socket_path (string): the socket file to prepare.

def _prepare_socket_file(self, socket_path, default_prefix):
        """Prepare the socket file for raylet and plasma.

        This method helps to prepare a socket file.
        1. Make the directory if the directory does not exist.
        2. If the socket file exists, raise exception.

        Args:
            socket_path (string): the socket file to prepare.
        """
        if socket_path is not None:
            if os.path.exists(socket_path):
                raise Exception("Socket file {} exists!".format(socket_path))
            socket_dir = os.path.dirname(socket_path)
            try_to_create_directory(socket_dir)
            return socket_path
        return self._make_inc_temp(
            prefix=default_prefix, directory_name=self._sockets_dir)