tests: Prepare for stricter NIC model validation

While using "definitely-not-virtio" as a model name is very
cute, it will also cause the relevant test to fail once we
introduce stricter validation.

Use "e1000", which is definitely not virtio but also a valid
model name, instead.
Signed-off-by: NAndrea Bolognani <abologna@redhat.com>

tests/qemuxml2argvdata/qemuxml2argv-tap-vhost-incorrect.xml

@@ -24,7 +24,7 @@
     <controller type='pci' index='0' model='pci-root'/>
     <interface type='user'>
       <mac address='52:54:00:e5:48:58'/>
-      <model type='definitely-not-virtio'/>
+      <model type='e1000'/>
       <driver name='vhost' queues='5'/>
       <backend tap='/dev/null' vhost='/dev/zero'/>
     </interface>

tests/qemuxml2xmloutdata/qemuxml2xmlout-tap-vhost-incorrect.xml

@@ -28,7 +28,7 @@
     <controller type='pci' index='0' model='pci-root'/>
     <interface type='user'>
       <mac address='52:54:00:e5:48:58'/>
-      <model type='definitely-not-virtio'/>
+      <model type='e1000'/>
       <backend tap='/dev/null'/>
       <address type='pci' domain='0x0000' bus='0x00' slot='0x03' function='0x0'/>
     </interface>