Send SIGABRT to child processes to instruct them to stop

def shutdown(self):
        """Send SIGABRT to child processes to instruct them to stop"""
        self.signal_children(signal.SIGABRT)

        # Wait a few iterations when trying to stop children before terminating
        waiting = 0
        while self.living_children:
            time.sleep(0.5)
            waiting += 1
            if waiting == self.MAX_SHUTDOWN_WAIT:
                self.signal_children(signal.SIGKILL)
                break