Utility method to retrieve a list of availability zones.

def availability_zone_list(request):
    """Utility method to retrieve a list of availability zones."""
    try:
        if api.cinder.extension_supported(request, 'AvailabilityZones'):
            return api.cinder.availability_zone_list(request)
        return []
    except Exception:
        exceptions.handle(request,
                          _('Unable to retrieve volumes availability zones.'))
        return []