Comment 4 for bug 1306602

@Huang: setting the default_schedule_zone does not solve the problem:

Problem:
-------

 1.) Setting default_schedule_zone to nova:

cat /etc/nova/nova.conf |grep schedule_zone
default_schedule_zone=nova

 2.) The function _handle_availability_zone in nova-api will return "nova" as AZ
 3.) But function host_passes() in availability_zone_filter.py has still "None" as result of props.get('availability_zone')