Add num_workers worker threads to the pool.

        ``poll_timout`` sets the interval in seconds (int or float) for how
        ofte threads should check whether they are dismissed, while waiting for
        requests.

def createWorkers(self, num_workers):
        """Add num_workers worker threads to the pool.

        ``poll_timout`` sets the interval in seconds (int or float) for how
        ofte threads should check whether they are dismissed, while waiting for
        requests.

        """
        for i in range(num_workers):
            self.workers.append(WorkerThread(self._requests_queue))