gitlab: 8.0.5 -> 8.5.0, service improvements

Updates gitlab to the current stable version and fixes a lot of features that
were broken, at least with the current version and our configuration.

Quite a lot of sweat and tears has gone into testing nearly all features and
reading/patching the Gitlab source as we're about to deploy gitlab for our
whole company.

Things to note:

 * The gitlab config is now written as a nix attribute set and will be
   converted to JSON. Gitlab uses YAML but JSON is a subset of YAML.
   The `extraConfig` opition is also an attribute set that will be merged
   with the default config. This way *all* Gitlab options are supported.

 * Some paths like uploads and configs are hardcoded in rails  (at least
   after my study of the Gitlab source). This is why they are linked from
   the Gitlab root to /run/gitlab and then linked to the  configurable
   `statePath`.

 * Backup & restore should work out of the box from another Gitlab instance.

 * gitlab-git-http-server has been replaced by gitlab-workhorse upstream.
   Push & pull over HTTPS works perfectly. Communication to gitlab is done
   over unix sockets. An HTTP server is required to proxy requests to
   gitlab-workhorse over another unix socket at
   `/run/gitlab/gitlab-workhorse.socket`.

 * The user & group running gitlab are now configurable. These can even be
   changed for live instances.

 * The initial email address & password of the root user can be configured.

Fixes #8598.

pkgs/applications/version-management/gitlab-workhorse/default.nix

@@ -0,0 +1,26 @@
+{ stdenv, fetchFromGitLab, git, go }:
+
+stdenv.mkDerivation rec {
+  version = "0.6.4";
+  name = "gitlab-workhorse-${version}";
+
+  srcs = fetchFromGitLab {
+    owner = "gitlab-org";
+    repo = "gitlab-workhorse";
+    rev = version;
+    sha256 = "09bs3kdmqi6avdak2nqma141y4fhfv050zwqqx7qh9a9hgkgwjxw";
+  };
+
+  buildInputs = [ git go ];
+
+  patches = [ ./remove-hardcoded-paths.patch ];
+
+  buildPhase = ''
+    make PREFIX=$out
+  '';
+
+  installPhase = ''
+    mkdir -p $out/bin
+    make install PREFIX=$out
+  '';
+}

pkgs/applications/version-management/gitlab-workhorse/remove-hardcoded-paths.patch

@@ -0,0 +1,12 @@
+diff --git a/internal/git/command.go b/internal/git/command.go
+index 0e5496c..5778294 100644
+--- a/internal/git/command.go
++++ b/internal/git/command.go
+@@ -16,6 +16,7 @@ func gitCommand(gl_id string, name string, args ...string) *exec.Cmd {
+ 	cmd.Env = []string{
+ 		fmt.Sprintf("HOME=%s", os.Getenv("HOME")),
+ 		fmt.Sprintf("PATH=%s", os.Getenv("PATH")),
++		fmt.Sprintf("GITLAB_SHELL_CONFIG_PATH=%s", os.Getenv("GITLAB_SHELL_CONFIG_PATH")),
+ 		fmt.Sprintf("LD_LIBRARY_PATH=%s", os.Getenv("LD_LIBRARY_PATH")),
+ 		fmt.Sprintf("GL_ID=%s", gl_id),
+ 	}