Fix RecentApps to properly load new thumbnails.

This fixes a bug introduced into recents by changes to
Carousel to prevent flashing in Music2.  Recents used
to rely on CarouselView.createCards() to reload the
thumbnails, which lead to flashing in Music2.   Now
the request to update is explicit.

Change-Id: I57d409c6b5969b788b52d4c1b3bbccab54d86bcb