'Start an instance.'

@check_instance_lock
@check_instance_host
@check_instance_cell
@check_instance_state(vm_state=[vm_states.STOPPED])
def start(self, context, instance):

    LOG.debug('Going    to    try    to    start    instance', instance=instance)
    instance.task_state = task_states.POWERING_ON
    instance.save(expected_task_state=[None])
    self._record_action_start(context, instance, instance_actions.START)
    self.compute_rpcapi.start_instance(context, instance)
