nix: move to repository root

Author: phip1611

integration-test/.envrc renamed to .envrc

@@ -5,10 +5,10 @@
         "homepage": null,
         "owner": "NixOS",
         "repo": "nixpkgs",
-        "rev": "219951b495fc2eac67b1456824cc1ec1fd2ee659",
-        "sha256": "065jy7qivlbdqmbvd7r9h97b23f21axmc4r7sqmq2h0j82rmymxv",
+        "rev": "576ecd43d3b864966b4423a853412d6177775e8b",
+        "sha256": "05gr8w09w7fqfi6zflx7df1n0hhsf8f4p9siikk3wb7k7by2d9sr",
         "type": "tarball",
-        "url": "https://github.com/NixOS/nixpkgs/archive/219951b495fc2eac67b1456824cc1ec1fd2ee659.tar.gz",
+        "url": "https://github.com/NixOS/nixpkgs/archive/576ecd43d3b864966b4423a853412d6177775e8b.tar.gz",
         "url_template": "https://github.com/<owner>/<repo>/archive/<rev>.tar.gz"
     }
 }

integration-test/nix/sources.json renamed to nix/sources.json

@@ -3,10 +3,15 @@ let
   pkgs = import sources.nixpkgs {};
 in
 pkgs.mkShell rec {
-  nativeBuildInputs = with pkgs; [
+  packages = with pkgs; [
+    # general
+    rustup
+    nixpkgs-fmt
+    niv
+
+    # integration test
     grub2
     qemu
-    rustup
     xorriso
   ];