tests/qtest/bios-tables-test: Make the test less verbose by default

tests/qtest/bios-tables-test: Make the test less verbose by default

We are facing the issues that our test logs in the gitlab CI are
too big (and thus cut off). The bios-tables-test is one of the few
qtests that prints many lines of output by default when running with
V=1, so it contributes to this problem. Almost all other qtests are
silent with V=1 and only print debug messages with V=2 and higher.
Thus let's change the bios-tables-test to behave more like the
other tests and only print the debug messages with V=2 (or higher).

Message-Id: <20230118125132.1694469-1-thuth@redhat.com>
Reviewed-by: Philippe Mathieu-Daudé <philmd@linaro.org>
Reviewed-by: Igor Mammedov <imammedo@redhat.com>
Reviewed-by: Daniel P. Berrangé <berrange@redhat.com>
Signed-off-by: Thomas Huth <thuth@redhat.com>