I found out that zopectl has a command named adduser. So instead of using the python script zpasswd.py to add a zope manager one can call:
#./zopectl adduser user_name user_password

I always used the "zopctl debug" and "zopectl test" but didnt know that zopectl has the adduser command.

Here is a list of all available commands:

# ./zopectl help

Documented commands (type help ):

========================================

EOF      fg          kill       quit     run    start   test

adduser  foreground  logreopen  reload   shell  status  wait

debug    help        logtail    restart  show   stop