Change to the privilege mode.

def enable(self, enable_password):
        """Change to the privilege mode."""
        if self.device.prompt[-1] == '#':
            self.log("Device is already in privileged mode")
            return

        events = [self.password_re, self.device.prompt_re, pexpect.TIMEOUT, pexpect.EOF]
        transitions = [
            (self.password_re, [0], 1, partial(a_send_password, enable_password), 10),
            (self.password_re, [1], -1, ConnectionAuthenticationError("Incorrect enable password",
                                                                      self.device.hostname), 0),
            (self.device.prompt_re, [0, 1, 2, 3], -1, a_expected_prompt, 0),
            (pexpect.TIMEOUT, [0, 1, 2], -1, ConnectionAuthenticationError("Unable to get privileged mode",
                                                                           self.device.hostname), 0),
            (pexpect.EOF, [0, 1, 2], -1, ConnectionError("Device disconnected"), 0)
        ]
        self.device.ctrl.send_command(self.enable_cmd)
        fsm = FSM("IOS-ENABLE", self.device, events, transitions, timeout=10, max_transitions=5)
        fsm.run()
        if self.device.prompt[-1] != '#':
            raise ConnectionAuthenticationError("Privileged mode not set", self.device.hostname)