'Used to enable/disable a service. For compute services, setting to
disabled stops new builds arriving on that host.
:param host_name: the name of the host machine that the service is
running
:param binary: The name of the executable that the service runs as
:param params_to_update: eg. {\'disabled\': True}
:returns: the service reference'

def service_update(self, ctxt, host_name, binary, params_to_update):

    (cell_name, host_name) = cells_utils.split_cell_and_item(host_name)
    response = self.msg_runner.service_update(ctxt, cell_name, host_name, binary, params_to_update)
    service = response.value_or_raise()
    service = cells_utils.add_cell_to_service(service, response.cell_name)
    return service
