Fix missing oslo.versionedobjects library option

This ensures the options for oslo.versionedobjects library are
included in the file generated by oslo-config-generator.

Change-Id: Ibaa8bcf06506f31d94a4e6bae9d9ea4c218da5de

Author: kajinamit

etc/nova/nova-config-generator.conf

@@ -14,6 +14,7 @@ namespace = oslo.service.service
 namespace = oslo.middleware
 namespace = oslo.concurrency
 namespace = oslo.reports
+namespace = oslo.versionedobjects
 namespace = keystonemiddleware.auth_token
 namespace = osprofiler
 namespace = os_vif