delete OS instance from this subnet
        :param os_instance: the OS instance to be deleted from this subnet
        :param sync: If sync=True(default) synchronize with Ariane server. If sync=False,
        add the OS instance object on list to be removed on next save().
        :return:

def del_os_instance(self, os_instance, sync=True):
        """
        delete OS instance from this subnet
        :param os_instance: the OS instance to be deleted from this subnet
        :param sync: If sync=True(default) synchronize with Ariane server. If sync=False,
        add the OS instance object on list to be removed on next save().
        :return:
        """
        LOGGER.debug("Subnet.del_os_instance")
        if not sync:
            self.osi_2_rm.append(os_instance)
        else:
            if os_instance.id is None:
                os_instance.sync()
            if self.id is not None and os_instance.id is not None:
                params = {
                    'id': self.id,
                    'osiID': os_instance.id
                }
                args = {'http_operation': 'GET', 'operation_path': 'update/osinstances/delete', 'parameters': params}
                response = SubnetService.requester.call(args)
                if response.rc != 0:
                    LOGGER.warning(
                        'Subnet.del_os_instance - Problem while updating subnet ' + self.name +
                        '. Reason: ' + str(response.response_content) + '-' + str(response.error_message) +
                        " (" + str(response.rc) + ")"
                    )
                else:
                    self.osi_ids.remove(os_instance.id)
                    os_instance.subnet_ids.remove(self.id)
            else:
                LOGGER.warning(
                    'Subnet.del_os_instance - Problem while updating subnet ' + self.name + '. Reason: OS instance ' +
                    os_instance.name + ' id is None or self.id is None'
                )