Ensure that test suite runs in the context of other distributions

I'm adding a test suite to Open Academy similar to the Panopoly one. Infact, we run the Panopoly tests as part of our own test suite to make sure all the Panopoly base goodness is working. As such, running the Panopoly tests in the context of a site that has other features/apps/content types etc enabled highlighted a small issue with the test suite. It assumes that 'Content Page' is the only content type and so when testing the live preview it doesn't explicitly select this content type from the list. In Panopoly thats fine because its the only content type so selected by default. But in Open Academy it is not the only content type and not selected by default making the test fail.