Explicitally use gevent for camera stream thread

import logging

import threading

import gevent

from abc import ABCMeta, abstractmethod

from collections import OrderedDict

        if not self.stream_active:

            # Spawn a greenlet to handle stream

            # start background frame thread

            self.thread = threading.Thread(target=self._thread)

            self.thread.daemon = True

            self.thread.start()

            self.thread = gevent.spawn(self._thread)

            # wait until frames are available

            logging.info("Waiting for frames")