websocket: use python logging module

WebSocketServer is a library module, as such, it cannot assume it can
write output to process stdout.

Python logging module is designed in order to allow subscribers to
handle the output out of modules. It is simple and generic mechanism to
separate between data producer and data handling.

Python logging API also has the nature of log level, so the verbose
parameter can probably be obsoleted in favor of logging level. And of
course the logging API has built in support for exception tracebacks, no
need for manual format.

The msg and vmsg were left for backward compatibility and to keep the
prefix of message, need to consider to drop these in favor of extra
parameter of python logging API.

Signed-off-by: Alon Bar-Lev <alon.barlev@gmail.com>