DLTS: Get NNI manager IP / port from endpoints

[Gerhut]

Previously, DLTS training service is using Kubernetes internal network to make to connections between different workers, which is not supported by all deployments.

This PR is switching it into job endpoints, which is officially supported by DLTS. Therefore, a manager job should:

1. Expose container port of RestServer to public as a job endpoint
2. Wait the exposed job endpoint be ready, and than get the hostname and host port (which is different from the container port) of the job endpoint
3. Start trial job with the hostname and host port as the address of RestServer.

[SparkSnail]

looks fine to me.