Random playback mode is not good for testing index changed signal,
because the same media might be played successively.
Calling show() might result in showFullScreen() on some platforms,
which is not expected by some video widget tests.
Change-Id: Ib47433fc6411b6dfa244a245aae508df5627ec62
Reviewed-by: Yoann Lopes <yoann.lopes@digia.com>