Disable cloud images

Supporting cloud VMs is not a goal for Apertis at the moment, we lack
several other pieces for that and it just wastes build time.

Signed-off-by: Emanuele Aina <emanuele.aina@collabora.com>

debian/config/amd64/none/defines

 [base]
 flavours:
  amd64
- cloud-amd64