Tests: Add standalone test configuration preamble to manual test

Add the boilerplate standalone test prelude to the manual featcheck
test, so that it can be configured with qt-cmake-private directly
without the qt-cmake-standalone-test script.

Change-Id: Ia959d1773530246ae783a892d37612f1e8b31c1b
Reviewed-by: Alexandru Croitor <alexandru.croitor@qt.io>