If a test fails it may trigger an assert in debug mode because
the delete wasn't performed. Move QWebEngine* objects to the stack
or use QScopedPointers to avoid these assertion fails.

Change-Id: Ic44c3fddc7cd9cf57a0e2d1c57e0a6fd99033e02
Reviewed-by: Peter Varga <pvarga@inf.u-szeged.hu>