Fix broken ProgressDialogTest to show how to test the setting of the message

The test was previously ignored because getMessage doesn't work in `ProgressDialog` (in response to #645). We decided *not* to make `getMessage()` work, as that would require adding more tricky shadowing that is dependent on the actual Android code. Rather we show a different testing strategy: use `getView()` and then query the `innerText()` to see that the message is somewhere in the view. 

There are still many `@Ignore`'d tests in the tests for the various Dialog classes. We may try to clean some of that up later this week. Cleaning up how Robolectric supports testing of dialogs in general might be in order as well.