Race condition with cvar changes during metric listener init

[PJB3005]

Triggered by trying to set metric properties in config presets in SS14. Config presets change property values during init and this causes the metric listener to try to initialize twice at once.

SpaceWizards.HttpListener.HttpListenerException (400): Failed to listen on prefix 'http://*:44880/metrics/' because it conflicts with an existing registration on the machine