test: write pre-rendered univeral html file to bazel bin dir

Server side rendered kitchen sync app was written inside the test sandbox execution directory, which is deleted after test execution when the is executed without `--sandbox_debug` option thus we couldn't retrieve the `index-prendered.html` file using the command `echo $(bazel info bazel-bin)/src/universal-app/index-prerendered.html`

src/universal-app/prerender.ts

@@ -3,7 +3,7 @@ import 'zone.js';
 
 import {renderModuleFactory} from '@angular/platform-server';
 import {readFileSync, writeFileSync} from 'fs';
-import {join} from 'path';
+import {dirname, join} from 'path';
 
 import {KitchenSinkRootServerModuleNgFactory} from './kitchen-sink-root.ngfactory';
 
@@ -16,10 +16,12 @@ const indexHtmlPath = require.resolve('./index.html');
 const result = renderModuleFactory(
     KitchenSinkRootServerModuleNgFactory,
     {document: readFileSync(indexHtmlPath, 'utf-8')});
+const runfilesDir = process.env.RUNFILES_DIR as string;
+const bazelOutDir = dirname(runfilesDir.replace(/sandbox\/[a-z0-9]+-sandbox\/[0-9]+\//, ''));
 
 result
   .then(content => {
-    const filename = join(__dirname, 'index-prerendered.html');
+    const filename = join(bazelOutDir, 'index-prerendered.html');
 
     console.log('Inspect pre-rendered page here:');
     console.log(`file://${filename}`);