def run_instances(self, xml_bytes):
        """
        Parse the reservations XML payload that is returned from an AWS
        RunInstances API call.

        @param xml_bytes: raw XML bytes with a C{RunInstancesResponse} root
            element.
        """
        root = XML(xml_bytes)
        # Get the security group information.
        groups = []
        for group_data in root.find("groupSet"):
            group_id = group_data.findtext("groupId")
            groups.append(group_id)
        # Create a reservation object with the parsed data.
        reservation = model.Reservation(
            reservation_id=root.findtext("reservationId"),
            owner_id=root.findtext("ownerId"),
            groups=groups)
        # Get the list of instances.
        instances = self.instances_set(root, reservation)
        return instances
Parse the reservations XML payload that is returned from an AWS
        RunInstances API call.

        @param xml_bytes: raw XML bytes with a C{RunInstancesResponse} root
            element.