Python 3 compatibility in test_multi_chunk_file

Author: ajdavis

test/test_grid_file.py

@@ -301,7 +301,7 @@ def test_close(self):
  f.close()
 
  def test_multi_chunk_file(self):
- random_string = 'a' * (DEFAULT_CHUNK_SIZE + 1000)
+ random_string = b('a') * (DEFAULT_CHUNK_SIZE + 1000)
 
  f = GridIn(self.db.fs)
  f.write(random_string)