python-hetzner: Update to new version 0.6.0.

This introduces the following changes:

 - Remove scraping of the Robot web interface for getting the server ID.
 - Display server number whenever appropriate.
 - Remove duplicate definition of exceptions.
 - Gracefully return if there are no subnets available.

Signed-off-by: aszlig <aszlig@redmoonstudios.org>