Split the environment concept into environment and layout

Initially, we had many environments with different nodes, etc. Nowadays,
they're all the same, except for network, image and flavour ids.

I've put the node stuff into environment/full.yaml and put the
environment specific stuff into a map file.

This depends on the corresponding change to python-jiocloud getting
merged first, though.
Sure, now that it's merged into master, no problem.