Fix hanging when loading pretrained models
- Fix hanging when loading pretrained models from the cache without having internet access. This is a widespread issue on supercomputers whose internal compute nodes are firewalled.
# [Codecov](https://codecov.io/gh/huggingface/transformers/pull/1568?src=pr&el=h1) Report
> Merging [#1568](https://codecov.io/gh/huggingface/transformers/pull/1568?src=pr&el=desc) into [master](https://codecov.io/gh/huggingface/transformers/commit/82f6abd98aaa691ca0adfe21e85a17dc6f386497?src=pr&el=desc) will **decrease** coverage by `0.02%`.
> The diff coverage is `100%`.

[![Impacted file tree graph](https://codecov.io/gh/huggingface/transformers/pull/1568/graphs/tree.svg?width=650&token=9qOlN6Hb1c&height=150&src=pr)](https://codecov.io/gh/huggingface/transformers/pull/1568?src=pr&el=tree)

```diff
@@            Coverage Diff             @@
##           master    #1568      +/-   ##
==========================================
- Coverage   86.16%   86.14%   -0.03%     
==========================================
  Files          91       91              
  Lines       13593    13593              
==========================================
- Hits        11713    11710       -3     
- Misses       1880     1883       +3
```


| [Impacted Files](https://codecov.io/gh/huggingface/transformers/pull/1568?src=pr&el=tree) | Coverage Δ | |
|---|---|---|
| [transformers/file\_utils.py](https://codecov.io/gh/huggingface/transformers/pull/1568/diff?src=pr&el=tree#diff-dHJhbnNmb3JtZXJzL2ZpbGVfdXRpbHMucHk=) | `74.17% <100%> (ø)` | :arrow_up: |
| [transformers/tests/modeling\_tf\_common\_test.py](https://codecov.io/gh/huggingface/transformers/pull/1568/diff?src=pr&el=tree#diff-dHJhbnNmb3JtZXJzL3Rlc3RzL21vZGVsaW5nX3RmX2NvbW1vbl90ZXN0LnB5) | `95.21% <0%> (-1.6%)` | :arrow_down: |

------

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> `Δ = absolute <relative> (impact)`, `ø = not affected`, `? = missing data`
> Powered by [Codecov](https://codecov.io/gh/huggingface/transformers/pull/1568?src=pr&el=footer). Last update [82f6abd...a2c8c8e](https://codecov.io/gh/huggingface/transformers/pull/1568?src=pr&el=lastupdated). Read the [comment docs](https://docs.codecov.io/docs/pull-request-comments).
<|||||>Ok, LGTM thanks