api: rename target_ateom_uid to worker_pod_uid in atelet.proto #2416

In internal/proto/ateletpb/atelet.proto, RunRequest, CheckpointRequest, RestoreRequest, and TerminateRequest identify the target worker pod using a field named target_ateom_uid:

message RunRequest {
  string target_ateom_uid = 1;
  ...
}

However, ateom does not have a UID of its own. The value ate-api-server passes in target_ateom_uid is assignment.GetWorkerPodUid() (the Kubernetes Pod UID of the worker pod, which atelet uses to locate the pod's kubelet directory and ateom socket). Across
ateapi.proto (Worker, WorkerAssignment, RegisterWorkerRequest), this identifier is named worker_pod_uid.

Proposal

1. In internal/proto/ateletpb/atelet.proto, rename target_ateom_uid to worker_pod_uid on RunRequest, CheckpointRequest, RestoreRequest, and TerminateRequest.
2. Regenerate protobufs and validation code (hack/update/codegen.sh, hack/protoc.sh).
3. Update all callers and handlers (cmd/ateapi, cmd/atelet, cmd/benchmarking/isolate/fake-atelet).

Benjamin Elder (@BenTheElder)