Many issues stems from `<nixpkgs>` not resolving anywhere or having the
wrong version, let's make it awfully obvious again here.
Towards #230.
Change-Id: If630e9616566e77143f028cdcfe0b7f00a1d486d
Signed-off-by: Raito Bezarius <raito@lix.systems>
`nix.full_path()` is the *built* path, not the *installed* path. in the
sandbox this point to a location that contains *only* `nix`, not any of
the old-cli symlinks. any test that needs them in path would thus fail.
Change-Id: Ia651db8d1151a84f8d1b52e8993f6db61b0fe104