[Update] Print training log in rank0

[shijungg]

Now the training log is printed in rank_last, it's not friendly to users if they change the amount of GPU node.

For example, a multi-node training job has master-0, worker-0, worker-1...
If we use 32 node(8 gpus each), we need to find the training log in worker-30.
Next time we use 64 node(8 gpus each), we need to find the training log in worker-62.

So print training log in rank0 is more friendly, we can just find the training log in master-0, no mater how many nodes we use for training.