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: I79ab4a6168b7931b783d542e44d9f3cae3351396

config-generator.conf

@@ -20,3 +20,4 @@ namespace = oslo.reports
 namespace = oslo.service.service
 namespace = oslo.service.periodic_task
 namespace = oslo.service.sslutils
+namespace = oslo.versionedobjects