tests/functional/test_vnc: Skip test if VNC support is not available These tests currently fail if VNC support has not been compiled into the QEMU binary. Let's add some checks to skip the tests in that case instead. Message-ID: <20250325064715.278876-1-thuth@redhat.com> Reviewed-by: Daniel P. Berrangé <berrange@redhat.com> Signed-off-by: Thomas Huth <thuth@redhat.com>