Two small logging improvements

The "starting" message is changed to match the Python one, and in case
the preparation fails, we also log the error (beside printing it on
stderr or writing it to the error reporting pipe), as at this time
logging is usually set up.

Signed-off-by: Iustin Pop <iustin@google.com>
Reviewed-by: Michael Hanselmann <hansmi@google.com>