fixing this article to be more generic about preview items and stop list...

...ing vm's as preview.

More specifically: Fixed the screenshot for the 'trial' link, removed the images listing specific preview services, and changed preview stuff to a note that "Some features are in preview. Click this preview link and select the items you are interested in". Hopefully this is generic enough that we don't have to churn this article for future things going into/out of preview.