test(spec): Control Server API secured via cross-pinning mTLS

. We are now leveraging nix for portable dependency handling.
. There are now three types of tests: client, server and end-to-end.
. server tests exercise the actual kapow server being tested, while the
requests are performed using the test steps.
. client tests exercise the actual kapow client being tested, while the
requests are served using the test steps.
. e2e test exercise the actual kapow program in its dual role of client
and server (¡como tiene que ser!).

Co-authored-by: Roberto Abdelkader Martínez Pérez <robertomartinezp@gmail.com>

spec/test/node-dependencies.nix

@@ -0,0 +1,17 @@
+# This file has been generated by node2nix 1.8.0. Do not edit!
+
+{pkgs ? import <nixpkgs> {
+    inherit system;
+  }, system ? builtins.currentSystem, nodejs ? pkgs."nodejs-12_x"}:
+
+let
+  nodeEnv = import ./node-env.nix {
+    inherit (pkgs) stdenv python2 utillinux runCommand writeTextFile;
+    inherit nodejs;
+    libtool = if pkgs.stdenv.isDarwin then pkgs.darwin.cctools else null;
+  };
+in
+import ./node-packages.nix {
+  inherit (pkgs) fetchurl fetchgit;
+  inherit nodeEnv;
+}