Add video type virtio for AArch64

Currently only "virtio" type is supported on AArch64, and the
other "virrus", "qxl" and "vga" don't work on AArch64 according to
libvirt upstream:
https://www.redhat.com/archives/libvir-list/2016-September/msg00546.html
Then this patch adds the virtio for AArch64 and tweaks the related test cases.

Closes-bug: #1710766

Change-Id: Iba8a1e671f2b5759b3d9178aa1871d0cf888b26b
Signed-off-by: Kevin Zhao <kevin.zhao@arm.com>

nova/tests/unit/virt/libvirt/test_driver.py

@@ -3685,6 +3685,9 @@ class LibvirtConnTestCase(test.NoDBTestCase,
 
         cfg = self._get_guest_config_with_graphics()
 
+        expect = {"ppc": "vga", "ppc64": "vga",
+                  "ppc64le": "vga", "aarch64": "virtio"}
+        video_type = expect.get(blockinfo.libvirt_utils.get_arch({}), "qxl")
         self.assertEqual(len(cfg.devices), 8)
         self.assertIsInstance(cfg.devices[0],
                               vconfig.LibvirtConfigGuestDisk)
@@ -3706,7 +3709,7 @@ class LibvirtConnTestCase(test.NoDBTestCase,
         self.assertEqual(cfg.devices[4].target_name, "com.redhat.spice.0")
         self.assertEqual(cfg.devices[4].type, 'spicevmc')
         self.assertEqual(cfg.devices[5].type, "spice")
-        self.assertEqual(cfg.devices[6].type, "qxl")
+        self.assertEqual(cfg.devices[6].type, video_type)
 
     def test_get_guest_config_with_vnc_no_keymap(self):
         self.flags(virt_type='kvm', group='libvirt')

nova/virt/libvirt/driver.py

@@ -4342,7 +4342,8 @@ class LibvirtDriver(driver.ComputeDriver):
                 allowed=ALLOWED_QEMU_SERIAL_PORTS, virt_type=virt_type)
 
     def _add_video_driver(self, guest, image_meta, flavor):
-        VALID_VIDEO_DEVICES = ("vga", "cirrus", "vmvga", "xen", "qxl")
+        VALID_VIDEO_DEVICES = ("vga", "cirrus", "vmvga",
+                               "xen", "qxl", "virtio")
         video = vconfig.LibvirtConfigGuestVideo()
         # NOTE(ldbragst): The following logic sets the video.type
         # depending on supported defaults given the architecture,
@@ -4360,6 +4361,10 @@ class LibvirtDriver(driver.ComputeDriver):
             # NOTE(ldbragst): PowerKVM doesn't support 'cirrus' be default
             # so use 'vga' instead when running on Power hardware.
             video.type = 'vga'
+        elif guestarch in (fields.Architecture.AARCH64):
+            # NOTE(kevinz): Only virtio device type is supported by AARCH64
+            # so use 'virtio' instead when running on AArch64 hardware.
+            video.type = 'virtio'
         elif CONF.spice.enabled:
             video.type = 'qxl'
         if image_meta.properties.get('hw_video_model'):