event: prevent unclosed file warning in print_ui_queue

event: prevent unclosed file warning in print_ui_queue

Use logger.addHandler(), rather than assigning an array of Handlers
to the loggers handlers property directly, to avoid a warning from
Python 3 about unclosed files:

$ bitbake
Nothing to do.  Use 'bitbake world' to build everything, or run 'bitbake --help' for usage information.
WARNING: /home/joshuagl/Projects/poky/bitbake/lib/bb/event.py:143: ResourceWarning: unclosed file <_io.TextIOWrapper name='/home/joshuagl/Projects/poky/build/tmp/log/cooker/qemux86/20161004094928.log' mode='a' encoding='UTF-8'>
  logger.handlers = [stdout]

Signed-off-by: Joshua Lock <joshua.g.lock@intel.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>