Fix #1015 (tokenizer defaults to use_lower_case=True when loading from trained models)
This PR fixes the issue where the tokenizer always defaults to `use_lower_case=True` when loading from trained models. It returns the control to the command-line arguments.
# [Codecov](https://codecov.io/gh/huggingface/pytorch-transformers/pull/1055?src=pr&el=h1) Report
> Merging [#1055](https://codecov.io/gh/huggingface/pytorch-transformers/pull/1055?src=pr&el=desc) into [master](https://codecov.io/gh/huggingface/pytorch-transformers/commit/c589862b783b94a8408b40c6dc9bf4a14b2ee391?src=pr&el=desc) will **not change** coverage.
> The diff coverage is `n/a`.

[![Impacted file tree graph](https://codecov.io/gh/huggingface/pytorch-transformers/pull/1055/graphs/tree.svg?width=650&token=9qOlN6Hb1c&height=150&src=pr)](https://codecov.io/gh/huggingface/pytorch-transformers/pull/1055?src=pr&el=tree)

```diff
@@          Coverage Diff           @@
##           master   #1055   +/-   ##
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  Coverage    79.6%   79.6%           
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  Files          42      42           
  Lines        6863    6863           
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  Hits         5463    5463           
  Misses       1400    1400
```



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<|||||>That's great, thanks @qipeng.

Do you think you could do the same fix on the  `run_glue` example?<|||||>Added tokenizer fix in `run_glue.py` and fixed `do_train` logic in `run_squad.py`<|||||>Great, thanks a lot @qipeng!