Fails to detect new users and create new qdiscs on demand when ratelimiting configured

[matt9j]

The current code assumes that all users will be in the database on startup, and fails to create new qdiscs for users that are later added to the system while operating. As a temporary workaround you can add new users and then restarting haulage to pick up the changes. The system does respond correctly to changes in the user configuration, and will successfully pick up changes to existing users without a restart.