python: Deal with str and byte differences.

python: Deal with str and byte differences.

Python 3 has separate types for strings and bytes.  Python 2 used the
same type for both.  We need to convert strings to bytes before writing
them out to a socket.  We also need to convert data read from the socket
to a string.

Signed-off-by: Russell Bryant <russell@ovn.org>
Acked-by: Ben Pfaff <blp@ovn.org>