Add registration url rewrite logic
Add registration url rewrite logic

Add registration url rewrite logic to enable end-to-end dev workflow.
If CATTLE_AGENT_LOCALHOST_REPLACE is set, localhost in the registration
url will be replaced with its value.

rancher/go-machine-service,ibuildthecloud/go-machine-service,rancherio/go-machine-service,rancherio/go-machine-service,cloudnautique/go-machine-service,cjellick/go-machine-service,ibuildthecloud/go-machine-service,cjellick/go-machine-service,rancher/go-machine-service,cloudnautique/go-machine-service