py3: make random topic name generation consistent across py2/py3 random.choice() (and others based on random.randint()) changed between py2 and py3 without a way to get the py2 behavior. However, random.random() did not change, so we can re-implement random.choice() based on that.

py3: convert str to bytes before passing to core exception

py3: convert opts keys to bytes before passing to core APIs

evolve: further clarify when update is performed