LockNotOwnedError: Cannot release a lock that's no longer owned

[michaelbukachi]

We started getting this error around a month ago. Not sure what changed, maybe something on Redis? Going through the source, in
redbeat/schedulers.py, I see we have this snippet:

def close(self):
        if self.lock:
            logger.debug('beat: Releasing Lock')
            self.lock.release()
            self.lock = None
        super(RedBeatScheduler, self).close()

Perhaps we can add an extra check i.e

def close(self):
        if self.lock:
            logger.debug('beat: Releasing Lock')
            # Add extra check
            if self.lock.owned() and self.lock.locked():
                self.lock.release()
            self.lock = None
        super(RedBeatScheduler, self).close()

Willing to do a quick PR for this.