Fix tst_QWebEngineFrame::setUrlWithFragment test

Change this test to rely on urlChanged() instead loadFinished(),
because we don't get loadFinished signal if the load was handled
by the same page.

Change-Id: I65aa06afa4512fa845074ad97b87ecba16da687e
Reviewed-by: Jocelyn Turcotte <jocelyn.turcotte@digia.com>