guest: Force qxl/vga more often

Letting libvirt choose gives us cirrus, which is really bad.
So for x86 for it more

tests/cli-test-xml/compare/virt-install-singleton-config-2.xml

@@ -153,6 +153,9 @@
       <backend type="emulator" version="2.0"/>
     </tpm>
     <graphics type="vnc" port="-1"/>
+    <video>
+      <model type="qxl"/>
+    </video>
     <watchdog model="ib700" action="pause"/>
     <memballoon model="virtio"/>
     <rng model="virtio">
@@ -331,6 +334,9 @@
       <backend type="emulator" version="2.0"/>
     </tpm>
     <graphics type="vnc" port="-1"/>
+    <video>
+      <model type="qxl"/>
+    </video>
     <watchdog model="ib700" action="pause"/>
     <memballoon model="virtio"/>
     <rng model="virtio">

tests/cli-test-xml/compare/virt-install-xen-hvm.xml

@@ -35,5 +35,8 @@
     </interface>
     <console type="pty"/>
     <graphics type="vnc" port="-1"/>
+    <video>
+      <model type="vga"/>
+    </video>
   </devices>
 </domain>

virtinst/guest.py

@@ -1189,7 +1189,9 @@ class Guest(XMLBuilder):
             if self.has_gl():
                 return "virtio"
             return "qxl"
-        if self._os_object.is_windows():
+        if self.os.is_hvm():
+            if self.conn.is_qemu():
+                return "qxl"
             return "vga"
         return None