'Create new image entry in the image service.  This new image
will be reserved for the compute manager to upload a snapshot
or backup.
:param context: security context
:param instance: nova.objects.instance.Instance object
:param name: string for name of the snapshot
:param image_type: snapshot | backup
:param extra_properties: dict of extra image properties to include'

def _create_image(self, context, instance, name, image_type, extra_properties=None):

    properties = {'instance_uuid': instance.uuid, 'user_id': str(context.user_id), 'image_type': image_type}
    properties.update((extra_properties or {}))
    image_meta = self._initialize_instance_snapshot_metadata(instance, name, properties)
    if (image_type == 'snapshot'):
        image_meta.pop('disk_format', None)
        image_meta.pop('container_format', None)
    return self.image_api.create(context, image_meta)
