Make sure Fluent is shutdown on exit

[mkundu1]

session.exit() is handled in a daemon thread (MonitorThread) which ensures shutdown of all streaming (non-daemon) threads. A daemon thread is terminated abruptly during Python process exit, after all non-daemon threads are exited). In the current code, the streaming threads are shut down after the server is exited within session.exit(). The MonitorThread shuts down immediately after shutting down the streaming threads without exiting the last server.

In this PR, a long-running thread is added which is exited at the end of session.exit() to ensure everything within session.exit() gets executed during exit.

Need to see how to unittest this (need a Python process exit).

[raph-luc]

LGTM, and nice that you are adding a test that can work both with and without containers as well

Very minor suggestion would be to rename _exit_evt to _exit_event just to make this var name clearer/obvious

[mkundu1]

LGTM, and nice that you are adding a test that can work both with and without containers as well

Very minor suggestion would be to rename _exit_evt to _exit_event just to make this var name clearer/obvious

Thanks for the suggestions, they are very helpful.