functional_tests/test_current_fillament.py does not actually test y-directed fillament

See lines:

```
    self.assertTrue(err_z < 4.7)      
    self.assertTrue(err_x < 4.7)      
    self.assertTrue(err_z < 4.7)      
```

Last one should be err_y. If changed, the test fails. There is probably something wrong with the rotation of the reference result.
