Port check_nagios_notifications.py to Python 3
    
    Saw from one of the emails this morning that this isn't running
    because there's no python2 on whatever system it was trying to
    run on. This ports it to Python 3 (thanks, 2to3) and cleans up
    the formatting (thanks, black). I tested it with a random sample
    file I found lying around the internet -
    https://github.com/bahamas10/node-nagios-status-parser/blob/master/status.dat
    and it seems to do what it's supposed to do.
    
    Signed-off-by: Adam Williamson <awilliam@redhat.com>