app: Spawn Headlamp server always detached and without shell

The way we were spawning the Headlamp server was different depending
on the platform and this led to issues where the server would be left
running after the app was quit.
This patch attempts to use a consistent set of options across
different platforms for launching the server.

app/electron/main.ts

@@ -39,12 +39,6 @@ function startServer(flags: string[] = []): ChildProcessWithoutNullStreams {
     ? path.resolve('../backend/headlamp-server')
     : path.join(process.resourcesPath, './headlamp-server');
 
-  const options = { shell: true, detached: false };
-  if (process.platform !== 'win32' && !isDev) {
-    // This makes the child processes a separate group, for easier killing.
-    options.detached = true;
-  }
-
   let serverArgs = [];
   if (!!args.kubeconfig) {
     serverArgs = serverArgs.concat(['--kubeconfig', args.kubeconfig]);
@@ -63,6 +57,12 @@ function startServer(flags: string[] = []): ChildProcessWithoutNullStreams {
   serverArgs = serverArgs.concat(flags);
   console.log('arguments passed to backend server', serverArgs);
 
+  // We run detached but not in shell, otherwise it's hard to make sure the
+  // server process gets killed. When changing these options, please make sure
+  // to test quitting the app in the different platforms and making sure the
+  // server process has been correctly quit.
+  const options = { detached: true };
+
   return spawn(serverFilePath, serverArgs, options);
 }