code: def describe_availability_zones(self, xml_bytes):
          
          results = []
          root = XML(xml_bytes)
          for zone_data in root.find("availabilityZoneInfo"):
              zone_name = zone_data.findtext("zoneName")
              zone_state = zone_data.findtext("zoneState")
              results.append(model.AvailabilityZone(zone_name, zone_state))
          return results
docs: Parse the XML returned by the C{DescribeAvailibilityZones} function.
  
          @param xml_bytes: XML bytes with a C{DescribeAvailibilityZonesResponse}
              root element.
          @return: a C{list} of L{AvailabilityZone}.
  
          TODO: regionName, messageSet