Python3 support for hot-backup.py

Hi developers.

I upgraded my server to the fedora core 32 which completely drop Python2.

So I prepare some quick and dirty patch (I really dont know Python at
all) which makes hot-backup.py script working again under Python3
environment.

Maybe some real python programmer is able improve my patch and include
all fixes to the trunk.

Regards,
Peter

-- 
Ing. Petr Petyovsky, Ph.D.
Brno University of Technology
Faculty of Electrical Engineering and Communication
Department of Control and Instrumentation
Technicka 3082/12, 616 00 Brno
Czech Republic
European Union