qemu: prepare existing test for change of the default video device type

The test relied implicitly on default video device being cirrus.  As we're
about to change that the test would start failing.  To avoid this, just make
the test's requirement explicit.
Reviewed-by: NCole Robinson <crobinso@redhat.com>
Signed-off-by: NPavel Mores <pmores@redhat.com>

tests/qemuxml2xmltest.c

@@ -372,7 +372,8 @@ mymain(void)
     DO_TEST("graphics-egl-headless-rendernode",
             QEMU_CAPS_DEVICE_CIRRUS_VGA,
             QEMU_CAPS_EGL_HEADLESS,
-            QEMU_CAPS_EGL_HEADLESS_RENDERNODE);
+            QEMU_CAPS_EGL_HEADLESS_RENDERNODE,
+            QEMU_CAPS_DEVICE_CIRRUS_VGA);
 
     DO_TEST("input-usbmouse", NONE);
     DO_TEST("input-usbtablet", NONE);