Use gevent sleep in mock camera

import numpy as np

from PIL import Image, ImageFont, ImageDraw

from datetime import datetime

import gevent

import logging

        # While the iterator is not closed

        try:

            while True:

                time.sleep(1)  # Only serve frames at 1fps

                gevent.sleep(1)  # Only serve frames at 1fps

                # Reset stream

                self.stream.seek(0)

                self.stream.truncate()