Strip the trailing router prompt from the output.

        :param a_string: Returned string from device
        :type a_string: str

def strip_prompt(self, a_string):
        """Strip the trailing router prompt from the output.

        :param a_string: Returned string from device
        :type a_string: str
        """
        response_list = a_string.split(self.RESPONSE_RETURN)
        last_line = response_list[-1]
        if self.base_prompt in last_line:
            return self.RESPONSE_RETURN.join(response_list[:-1])
        else:
            return a_string