logging: make sure logging is done only once.
logging: make sure logging is done only once.

The root_logger.handlers = list() was not nice, because other people
may have register log handlers.

Simply calling addHanlder caused the ColorLogHandler to be added several
times, causing the logs to be printed several times too.

This should be a nice fix.

aldebaran/qibuild,aldebaran/qibuild,dmerejkowsky/qibuild,aldebaran/qibuild,dmerejkowsky/qibuild,dmerejkowsky/qibuild,aldebaran/qibuild,dmerejkowsky/qibuild,dmerejkowsky/qibuild