Finds the current network device prompt, last line only.

        :param delay_factor: See __init__: global_delay_factor
        :type delay_factor: int

def find_prompt(self, delay_factor=1):
        """Finds the current network device prompt, last line only.

        :param delay_factor: See __init__: global_delay_factor
        :type delay_factor: int
        """
        delay_factor = self.select_delay_factor(delay_factor)
        self.clear_buffer()
        self.write_channel(self.RETURN)
        time.sleep(delay_factor * 0.1)

        # Initial attempt to get prompt
        prompt = self.read_channel()
        if self.ansi_escape_codes:
            prompt = self.strip_ansi_escape_codes(prompt)

        # Check if the only thing you received was a newline
        count = 0
        prompt = prompt.strip()
        while count <= 10 and not prompt:
            prompt = self.read_channel().strip()
            if prompt:
                if self.ansi_escape_codes:
                    prompt = self.strip_ansi_escape_codes(prompt).strip()
            else:
                self.write_channel(self.RETURN)
                time.sleep(delay_factor * 0.1)
            count += 1

        # If multiple lines in the output take the last line
        prompt = self.normalize_linefeeds(prompt)
        prompt = prompt.split(self.RESPONSE_RETURN)[-1]
        prompt = prompt.strip()
        if not prompt:
            raise ValueError("Unable to find prompt: {}".format(prompt))
        time.sleep(delay_factor * 0.1)
        self.clear_buffer()
        return prompt