nixos/cloudinit: add cloudinit test

An iso containing metadatas is created and attached as a cdrom to the
qemu VM used for this test.

The cloudinit service is enabled. The test case ensures the root
authorized_keys file is populated and the cloudinit write_file module is
working well.

nixos/release.nix

···
   tests.cadvisor = hydraJob (import tests/cadvisor.nix { system = "x86_64-linux"; });
   tests.chromium = (callSubTests tests/chromium.nix { system = "x86_64-linux"; }).stable;
   tests.cjdns = callTest tests/cjdns.nix {};
+  tests.cloud-init = callTest tests/cloud-init.nix {};
   tests.containers-ipv4 = callTest tests/containers-ipv4.nix {};
   tests.containers-ipv6 = callTest tests/containers-ipv6.nix {};
   tests.containers-bridge = callTest tests/containers-bridge.nix {};

nixos/tests/cloud-init.nix

···
+{ system ? builtins.currentSystem }:
+
+with import ../lib/testing.nix { inherit system; };
+with import ../lib/qemu-flags.nix;
+with pkgs.lib;
+
+let
+  metadataDrive = pkgs.stdenv.mkDerivation {
+    name = "metadata";
+    buildCommand = ''
+      mkdir -p $out/iso
+
+      cat << EOF > $out/iso/user-data
+      #cloud-config
+      write_files:
+      -   content: |
+                cloudinit
+          path: /tmp/cloudinit-write-file
+      EOF
+
+      cat << EOF > $out/iso/meta-data
+      instance-id: iid-local01
+      local-hostname: "test"
+      public-keys:
+          - "should be a key!"
+      EOF
+      ${pkgs.cdrkit}/bin/genisoimage -volid cidata -joliet -rock -o $out/metadata.iso $out/iso
+      '';
+  };
+in makeTest {
+  meta = with pkgs.stdenv.lib.maintainers; {
+    maintainers = [ lewo ];
+  };
+  machine =
+    { config, pkgs, ... }:
+    {
+      virtualisation.qemu.options = [ "-cdrom" "${metadataDrive}/metadata.iso" ];
+      services.cloud-init.enable = true;
+    };
+  testScript = ''
+     $machine->start;
+     $machine->waitForUnit("cloud-init.service");
+     $machine->succeed("cat /tmp/cloudinit-write-file | grep -q 'cloudinit'");
+
+     $machine->waitUntilSucceeds("cat /root/.ssh/authorized_keys | grep -q 'should be a key!'");
+  '';
+}