oeqa/utils/httpserver: connect up the request logging

Call logger.info() in the log_message handler so that we get request
logging, and hopefully even error messages.

Create a child logger to be neat and compartmentalise the logging.

Add a __main__ entrypoint so this class can be exercised outside of oeqa.

Remove unused traceback import.

Signed-off-by: Ross Burton <ross.burton@arm.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>