tests: Add negative test for Intel IOMMU

Make sure validation is working as intended by trying to use
Intel IOMMU with the i440fx machine type, though we know it's
a q35-only feature, and expecting an error to be returned.
Signed-off-by: NAndrea Bolognani <abologna@redhat.com>
Reviewed-by: NJán Tomko <jtomko@redhat.com>

tests/qemuxml2argvdata/intel-iommu-wrong-machine.xml

+<domain type='qemu'>
+  <name>QEMUGuest1</name>
+  <uuid>c7a5fdbd-edaf-9455-926a-d65c16db1809</uuid>
+  <memory unit='KiB'>219100</memory>
+  <currentMemory unit='KiB'>219100</currentMemory>
+  <vcpu placement='static'>1</vcpu>
+  <os>
+    <type arch='x86_64' machine='pc'>hvm</type>
+    <boot dev='hd'/>
+  </os>
+  <clock offset='utc'/>
+  <on_poweroff>destroy</on_poweroff>
+  <on_reboot>restart</on_reboot>
+  <on_crash>destroy</on_crash>
+  <devices>
+    <emulator>/usr/bin/qemu-system-x86_64</emulator>
+    <controller type='pci' index='0' model='pci-root'/>
+    <controller type='usb' index='0' model='none'/>
+    <input type='mouse' bus='ps2'/>
+    <input type='keyboard' bus='ps2'/>
+    <memballoon model='none'/>
+    <iommu model='intel'/>
+  </devices>
+</domain>

tests/qemuxml2argvtest.c

@@ -2812,6 +2812,7 @@ mymain(void)
     DO_TEST_CAPS_LATEST("intel-iommu-caching-mode");
     DO_TEST_CAPS_LATEST("intel-iommu-eim");
     DO_TEST_CAPS_LATEST("intel-iommu-device-iotlb");
+    DO_TEST_FAILURE("intel-iommu-wrong-machine", NONE);
 
     DO_TEST("cpu-hotplug-startup", QEMU_CAPS_QUERY_HOTPLUGGABLE_CPUS);
     DO_TEST_PARSE_ERROR("cpu-hotplug-granularity",