nixos-install: Respect...

nixos-install: Respect /home/shlevy/src:/nix/var/nix/profiles/per-user/root/channels/nixos:nixpkgs=/etc/nixos/nixpkgs:nixos=/etc/nixos/nixos:nixos-config=/etc/nixos/configuration.nix:services=/etc/nixos/services to find the nixos and nixpkgs sources, only copy the nixos channel if it exists