Comment 1 for bug 1640635

cloudinit/stages.py uses 'net.is_disabled_cfg()'.

I just verified on a fresh lxc container.

 * boot system
 * lxc exec x1
   % echo "network: {config: disabled}" > /etc/cloud/cloud.cfg.d/99-disable-network-config.cfg
   % rm /etc/network/interfaces.d/50-cloud-init.cfg
   % reboot
 * lxc exec x1
   % cat /etc/network/interfaces.d/50-cloud-init.cfg
   cat: /etc/network/interfaces.d/50-cloud-init.cfg: No such file or directory
   % dpkg-query --show cloud-init
   cloud-init 0.7.8-1-g3705bb5-0ubuntu1~16.04.3

   % grep "INFO.*disabled" /var/log/cloud-init.log
   Nov 10 02:07:59 xt1 [CLOUDINIT] stages.py[INFO]: network config is disabled by system_cfg
   Nov 10 02:08:00 xt1 [CLOUDINIT] stages.py[INFO]: network config is disabled by system_cfg

So it seems not completely broken there.