Attempt to become root.

def config_mode(self, config_command="sudo su"):
        """Attempt to become root."""
        delay_factor = self.select_delay_factor(delay_factor=1)
        output = ""
        if not self.check_config_mode():
            output += self.send_command_timing(
                config_command, strip_prompt=False, strip_command=False
            )
            if "Password:" in output:
                output = self.write_channel(self.normalize_cmd(self.secret))
            self.set_prompt(prompt_terminator="#")
            time.sleep(1 * delay_factor)
            self.set_base_prompt()
            if not self.check_config_mode():
                raise ValueError("Failed to configuration mode")
        return output