message: Set `fail_fast` to false for `CompleteGroup` RPC.
  In multi-worker sync training, this is the first RPC issued by workers, and it should block while peers are starting up.
diff: @@ -19,7 +19,6 @@ limitations under the License.
  #include "grpcpp/generic/generic_stub.h"
  #include "grpcpp/grpcpp.h"
  -
  #include "tensorflow/core/common_runtime/process_util.h"
  #include "tensorflow/core/distributed_runtime/rpc/grpc_client_cq_tag.h"
  #include "tensorflow/core/distributed_runtime/rpc/grpc_state.h"
  @@ -176,7 +175,8 @@ class GrpcRemoteWorker : public WorkerInterface {
  const CompleteGroupRequest* request,
  CompleteGroupResponse* response,
  StatusCallback done) override {
  - IssueRequest(request, response, completegroup_, std::move(done), call_opts);
  + IssueRequest(request, response, completegroup_, std::move(done), call_opts,
  + /*fail_fast=*/false);
  }
  void CompleteInstanceAsync(CallOptions* call_opts,
  