Move method to the FileTestUtil

Signed-off-by: Nico Rutishauser <nr@hotmail.ch>
Only use chunk size at generation of random file

Signed-off-by: Nico Rutishauser <nr@hotmail.ch>
Add tests for the FileChunkUtil

and improve the util with found issues

Signed-off-by: Nico Rutishauser <nr@hotmail.ch>