[seq2seq] fix logger format for non-main process

[stas00]

Currently, in finetune_trainer.py non-main process doesn't have any formatting at all, so we end up with:

[WARNING|modeling_t5.py:1645] 2021-01-30 20:01:37,246 >> [p0] got MPU
[WARNING|modeling_t5.py:1646] 2021-01-30 20:01:37,246 >> [p0] DP group [0]
[p1] got MPU
[p1] DP group [1]

as you can see the 2nd process in DDP misses formatting in logger.

this PR fixes it.

I looked in the take-over version run_seq2seq.py if it needed to be fixed too and it doesn't have these function calls, not sure why. They appear to be needed, unless they get called elsewhere.

@sgugger, @patil-suraj

[sgugger]

@LysandreJik knows better for the centralized logging system so I'll defer to him.

[LysandreJik]

Indeed, good catch! All processes should share the handler/formatting options, even if they have different verbosity.

Thanks @stas00!