'Plug virtual interfaces (VIFs) into the given `instance` at
instance boot time.
The counter action is :func:`unplug_vifs`.
:param nova.objects.instance.Instance instance:
The instance which gets VIFs plugged.
:param nova.network.model.NetworkInfo network_info:
The object which contains information about the VIFs to plug.
:return: None'

def plug_vifs(self, instance, network_info):

    raise NotImplementedError()
