Test code cannot find _data dir

It seems that because the ct task is setting the ebin dir to something that includes `test_beams`, Common Test expects to find the module_name_SUITE_data directory there as well. However, that is not the case, it is in the original source directory, and appears to be copied to a directory named `test` that is next to `test_beams`. As such, the test code fails to find the data files.

While one can work around this in the test code, it would seem better for the ct task to set the `data_dir` property when invoking ct so that it has the correct path.