message: Improve the error message printed when a WorkerService::GetStatus() call fails on session creation.
diff: @@ -269,7 +269,8 @@ class DeviceFinder {
  mutex_lock l(mu_);
  seen_targets_[target_index] = true;
  if (!s.ok()) {
  - LOG(ERROR) << "Master init: " << s;
  + LOG(ERROR) << "CreateSession failed because worker "
  + << targets_[target_index] << " returned error: " << s;
  status_.Update(s);
  } else {
  found_.insert(found_.end(), devices->begin(), devices->end());
  