tests: fix xen-related tests

My commit 6879be4 moved the addition of the implicit video device
from the XML parser to the PostParse function, but did not regenerate
all the tests.

tests/xlconfigdata/test-disk-positional-parms-partial.xml

@@ -51,5 +51,8 @@
     <graphics type='vnc' port='-1' autoport='yes' listen='127.0.0.1'>
       <listen type='address' address='127.0.0.1'/>
     </graphics>
+    <video>
+      <model type='cirrus' heads='1' primary='yes'/>
+    </video>
   </devices>
 </domain>