libvirt: Add objects and notifications for USB controller model.

This patch adds just the objects and notifications required to
support an extra spec to configure a USB controller inside
the guest. This is useful for SPICE consoles using the native
protocol.

Change-Id: I791b16c5bf0e860a188783c863e95dc423998b0a
Signed-off-by: Michael Still <mikal@stillhq.com>

doc/notification_samples/common_payloads/ImageMetaPropsPayload.json

@@ -4,5 +4,5 @@
         "hw_architecture": "x86_64"
     },
     "nova_object.name": "ImageMetaPropsPayload",
-    "nova_object.version": "1.16"
-}
+    "nova_object.version": "1.17"
+}