Problem/Motivation
While wokring on #3274066: Node tests should not rely on Classy it was determined that Drupal\Tests\node\Functional\PagePreviewTest could not be updated to use Stark as the theme.
The main reason for this is that there is an assertion in PagePreviewTest::testPagePreview() that was added as test coverage for the bug #2736391: Node type body class is not present on node preview page.
Proposed resolution
Do it once starterkit is stable.
Remaining tasks
1. Make starterkit stable
2. Do it
User interface changes
None
API changes
None
Data model changes
None
Release notes snippet
None
