examples/tests/whiteboard.py: remove chdir into datadir

The whiteboard test is an example test, and, since, we're about to
deprecate the datadir attribute, let's remote this call to chdir.

If we believe that's necessary to stress this part of the API, let's
write a (non-example) test for that.
Signed-off-by: NCleber Rosa <crosa@redhat.com>

examples/tests/whiteboard.py

 #!/usr/bin/env python
 
 import base64
-import os
 
 from six.moves import xrange as range
 
@@ -21,7 +20,6 @@ class WhiteBoard(Test):
     """
 
     def test(self):
-        os.chdir(self.datadir)    # Just to stress out Avocado
         data_file = self.params.get('whiteboard_data_file', default='')
         data_size = self.params.get('whiteboard_data_size', default='10')
         if data_file: