Use logging module for the QMP debug messages.  The only scripts
that set debug=True are iotests.py and guestperf/engine.py, and
they already call logging.basicConfig() to set up logging.

Scripts that don't configure logging are safe as long as they
don't need debugging output, because debug messages don't trigger
the "No handlers could be found for logger" message from the
Python logging module.

Scripts that already configure logging but don't use debug=True
(e.g. scripts/vm/basevm.py) will get QMP debugging enabled for
free.

Cc: "Alex Bennée" <alex.bennee@linaro.org>
Cc: Fam Zheng <famz@redhat.com>
Cc: "Philippe Mathieu-Daudé" <f4bug@amsat.org>
Signed-off-by: NEduardo Habkost <ehabkost@redhat.com>
Message-Id: <20171005172013.3098-3-ehabkost@redhat.com>
Reviewed-by: NLukáš Doktor <ldoktor@redhat.com>
Signed-off-by: NEduardo Habkost <ehabkost@redhat.com>