[examples] replicate the new `--log_level` feature to all trainer-based pytorch examples
https://github.com/huggingface/transformers/pull/12276 introduced a new `--log_level` feature, which now allows users to set their desired log level via CLI or TrainingArguments. 

`run_translation.py` was used as a "model" for other examples.

Now we need to replicate this to all other Trainer-based examples under examples/pytorch/, the 3 changes are
1. importing datasets
2. using `training_args.get_node_log_level()`  and setting log_level in 3 modules
3. replacing `datasets` object name with `raw_datasets`, since otherwise we have a conflict with `datasets` the module.

and the relevant diff is [here](https://github.com/huggingface/transformers/pull/12276/files?file-filters%5B%5D=.py#diff-09777f56cee1060a535a72ce99a6c96cdb7f330c8cc3f9dcca442b3f7768237a)

and of course since we don't quite have extensive tests for examples, you can just test with a staple cmd from the corresponding README.md with `--log_level=error` and check that almost all logs are gone.

This is open to all.

And thank you.
Can I take this?<|||||>Yes, of course! Thank you, @bhadreshpsavani <|||||>@bhadreshpsavani, once https://github.com/huggingface/transformers/pull/12309 gets merged, please rebase your branch and rename
```
-    get_node_log_level()
+    get_process_log_level()
```

Thank you!<|||||>ok, it's merged now.<|||||>Thanks!<|||||>How can I contribute?<|||||>Please refer to https://github.com/huggingface/transformers/blob/master/CONTRIBUTING.md