tests/functional: honour requested test VM name in QEMUMachine

tests/functional: honour requested test VM name in QEMUMachine

The functional test case class is going to the trouble of passing
around a machine name, but then fails to give this QEMUMachine. As
a result, QEMUMachine will create a completely random name. Since
log file names match the machine name, this results in log files
accumulating over time.

Reviewed-by: Thomas Huth <thuth@redhat.com>
Signed-off-by: Daniel P. Berrangé <berrange@redhat.com>
Message-Id: <20241121154218.1423005-11-berrange@redhat.com>
Signed-off-by: Alex Bennée <alex.bennee@linaro.org>
Message-Id: <20241121165806.476008-11-alex.bennee@linaro.org>