Update test logic to reflect new REST API featured image format.
Remove search for attachments for featured image test.

The featuredImageFromPostDictionary no longer searches on attachments it goes directly to the content of the post.
Make defaultAccount a variable to make it easier to debug.

It looks there is race condition between this test and the simulator starting the app or the saving of the context.
When pausing for debug the test they succeed if they run without pause they fail.