atexit hook prevents garbage collection from working

[devicenull]

See http://stackoverflow.com/questions/16333054/what-are-the-implications-of-registering-an-instance-method-with-atexit-in-pytho

You're using atexit here to log out, https://github.com/tenable/nessrest/blob/master/nessrest/ness6rest.py#L113

However, this prevents the Scanner object from ever going through garbage collection. That means in a long-running app, it'll stick around forever.