Fixed JUnit launcher test

I finally fixed the JUnit launcher test. The problem was indeed the project was not compiled, so the JUnit classpath referenced nonexistent files/folders. I managed to compile the project, but it is a little bit tricky, since a simple `project.build()` call was not enough, so i had to use a workaround. Please see the comments of #235 of my really long investigation...

With the modified `buildAndroidProject()`method, the `ignoreTestBuildDirectoryContainsCompiledClasses` test would pass, too. I did not re-enable it because i was not 100% sure why did you disable it in the first place.