morph deployment should be independent of NIX_PATH

Created by: exarkun

The build of the morph-managed networks depends on what nixpkgs is available when morph is invoked. This is just what the README says will happen. However, having to remember the extra step of setting NIX_PATH correctly before doing any deployment management adds another place for human error in the process.

This step should be removed so that morph deploy ... can be used without taking any extra steps in the deployment environment.

One way to do this would be to encode the version of nixpkgs into the Nix deployment configuration itself. morph/lib/make-grid.nix currently does import <nixpkgs> { } which could probably be changed to import a specific version of nixpkgs instead.