tests/qtest/qom-test: Stop spamming the test log

tests/qtest/qom-test: Stop spamming the test log

We are still facing the issues that our test logs in the gitlab CI
are too big (and thus cut off). A huge part is still caused by the
qom-test that prints the path and name of each object it looks at
by default. That's too much. Let's be silent by default, and only
print the object path+name when running with V=2 (and the properties
only with V=3 and higher).

Message-Id: <20230118122557.1668860-1-thuth@redhat.com>
Reviewed-by: Daniel P. Berrangé <berrange@redhat.com>
Reviewed-by: Philippe Mathieu-Daudé <philmd@linaro.org>
Signed-off-by: Thomas Huth <thuth@redhat.com>