Moves Nova v3 API enable config to group

https://review.openstack.org/#/c/29487/ moves the Nova v3 API
enable flag into its own config group. And renames it to just
"enable". This changeset follows that change. As we do not yet
gate on any Nova V3 API tests we don't need to keep the old setting
around.

Change-Id: If1592cd7b9aad24b6d010870a5fb6bcc60efb8ac
diff --git a/lib/nova b/lib/nova
index 809f56c..bb94aff 100644
--- a/lib/nova
+++ b/lib/nova
@@ -439,7 +439,7 @@
     iniset $NOVA_CONF DEFAULT libvirt_type "$LIBVIRT_TYPE"
     iniset $NOVA_CONF DEFAULT libvirt_cpu_mode "none"
     iniset $NOVA_CONF DEFAULT instance_name_template "${INSTANCE_NAME_PREFIX}%08x"
-    iniset $NOVA_CONF DEFAULT osapi_v3_enabled "True"
+    iniset $NOVA_CONF osapi_v3 enabled "True"
 
     if is_service_enabled n-api; then
         iniset $NOVA_CONF DEFAULT enabled_apis "$NOVA_ENABLED_APIS"