scripts: Remove debug parameter from QEMUMachine

All scripts that use the QEMUMachine and QEMUQtestMachine classes
(device-crash-test, tests/migration/*, iotests.py, basevm.py)
already configure logging.

The basicConfig() call inside QEMUMachine.__init__() is being
kept just to make sure a script would still work if it didn't
configure logging.

Signed-off-by: Eduardo Habkost <ehabkost@redhat.com>
Message-Id: <20171005172013.3098-4-ehabkost@redhat.com>
Reviewed-by: Lukáš Doktor <ldoktor@redhat.com>
Signed-off-by: Eduardo Habkost <ehabkost@redhat.com>