Make Portable ULR use workerId in GRPC channel

[kennknowles]

The internal implementation of Data service uses workerId make sure that 

https://github.com/apache/beam/blob/master/runners/java-fn-execution/src/main/java/org/apache/beam/runners/fnexecution/data/GrpcDataService.java

Also uses workerId.

Imported from Jira BEAM-4219. Original Jira may contain additional context.
Reported by: angoenka.