Nova: Update MVP values to reflect removal of oslo-genconfig tool

This PS updates the Nova MVP values to reflect the removal of
the oslo-genfig tool.

Change-Id: Ibb5c2b4e97d119da138fe1ba853137f517703bcd

tools/overrides/mvp/nova.yaml

@@ -17,21 +17,13 @@ ceph:
 
 conf:
   nova:
-    default:
-      oslo:
-        log:
-          debug: false
     libvirt:
-      nova:
+      images_type: null
-        conf:
+      images_rbd_pool: null
-          images_type: null
+      images_rbd_ceph_conf: null
-          images_rbd_pool: null
+      rbd_user: null
-          images_rbd_ceph_conf: null
+      rbd_secret_uuid: null
-          rbd_user: null
+      disk_cachemodes: null
-          rbd_secret_uuid: null
+      hw_disk_discard: null
-          disk_cachemodes: null
-          hw_disk_discard: null
     upgrade_levels:
-      nova:
+      compute: null
-        conf:
-          compute: null