refactor junitTest cleanup

after executing the whole catroidTest package there were two testprojects in pocketcode folder.
calling TestUtils.deleteTestProjects deletes the project with DEFAULT_TEST_PROJECT name, and can be used with additional parameter to delete a certain project (https://github.com/Catrobat/Catroid/blob/master/catroidTest/src/org/catrobat/catroid/test/utils/TestUtils.java#L195)