If the service_url is set to http://{server-1}:8080,{server-2}:8080,{server-3}:8080 when initialize-cluster-metadata, the cluster_url will be "{server-1}:8080,{server-2}:8080,{server-3}:8080".
And the string "{server-1}:8080,{server-2}:8080,{server-3}:8080" isn't a standard url.

* fix culster_url which may be set as a list

* use random to select service_url