get_from_cache in file_utils.py gobbles up error in making url requests
Author: SinghB
Pull request: no

# 🐛 Bug
No information from the package on SSL error encountered, making it difficult to troubleshoot or figure out a workaround

## Information
When trying to do:
`TFAutoModelWithLMHead.from_pretrained("t5-small")`

Get an error:
`TypeError: stat: path should be string, bytes, os.PathLike or integer, not NoneType`

The above is a result of an SSL error encountered when trying to fetch the model, however, since the exception handling isn't proper within file_utils.py I don't come to know of it, unless I debug.

Model I am using (Bert, XLNet ...): T5

Language I am using the model on (English, Chinese ...): English

The problem arises when using:
* [ x] the official example scripts: (give details below)
* [ ] my own modified scripts: (give details below)

https://huggingface.co/transformers/usage.html#summarization

The tasks I am working on is:
* [ ] an official GLUE/SQUaD task: (give the name)
* [ x] my own task or dataset: (give details below)
Just getting familiar with transformers for summarization

## To reproduce
You need a machine with an expired certificate for proxy etc.

Steps to reproduce the behavior:

1. See information above

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## Expected behavior
If there has been an issue in fetching the pre-trained model from s3 bucket etc. I should get an error to that effect.

## Environment info
<!-- You can run the command `transformers-cli env` and copy-and-paste its output below.
     Don't forget to fill out the missing fields in that output! -->
     
- `transformers` version: 2.10.0
- Platform: Windows 10
- Python version: 3.7.4
- PyTorch version (GPU?): NA
- Tensorflow version (GPU?): 2.0.0 (Yes)
- Using GPU in script?: No
- Using distributed or parallel set-up in script?: No


Comments:
This issue has been automatically marked as stale because it has not had recent activity. It will be closed if no further activity occurs. Thank you for your contributions.


Ran into this today, this is a major issue behind corporate proxy/CA self signed certs. @SinghB  maybe you can reopen this, I'm not sure who to `@mention`?

```python
get_from_cache(
  # ...
  etag = None
    if not local_files_only:
        try:
            response = requests.head(url, allow_redirects=True, proxies=proxies, timeout=etag_timeout)
            if response.status_code == 200:
                etag = response.headers.get("ETag")
        except (EnvironmentError, requests.exceptions.Timeout):
            # etag is already None
            # THIS ALSO SWALLOWS ALL OTHER NON "404" ERRORS (e.g. SSL, Proxy, etc.)
            pass
  # ....
```

Yes I want to track and solve that issue in the next couple of weeks.

+1 from me.

Currently I get this error message:

```
OSError: Can't load weights for 'bert-base-uncased'. Make sure that:

- 'bert-base-uncased' is a correct model identifier listed on 'https://huggingface.co/models'

- or 'bert-base-uncased' is the correct path to a directory containing a file named one of pytorch_model.bin, tf_model.h5, model.ckpt.
```

But if I add a `raise` after the `# etag is already None` comment in stadelmanma's snippet, I see:

```
requests.exceptions.SSLError: HTTPSConnectionPool(host='cdn.huggingface.co', port=443): Max retries exceeded with url: /bert-base-uncased-pytorch_model.bin (Caused by SSLError(SSLCertVerificationError(1, '[SSL: CERTIFICATE_VERIFY_FAILED] certificate verify failed: unable to get local issuer certificate (_ssl.c:1056)')))
```

This leads to confusing debugging... the behavior of this error shouldn't be to indicate to the user that models like `bert-based-uncased` don't exist.

Hi @julien-c , I'm having the same issue as @stadelmanma  (I'm behind a coporate proxy as well)

```  File "/home/USER/anaconda3/envs/codebert/lib/python3.7/site-packages/transformers/configuration_utils.py", line 376, in from_pretrained
    config_dict, kwargs = cls.get_config_dict(pretrained_model_name_or_path, **kwargs)
  File "/home/USER/anaconda3/envs/codebert/lib/python3.7/site-packages/transformers/configuration_utils.py", line 436, in get_config_dict
    raise EnvironmentError(msg)
OSError: Can't load config for 'microsoft/deberta-base'. Make sure that:

- 'microsoft/deberta-base' is a correct model identifier listed on 'https://huggingface.co/models'

- or 'microsoft/deberta-base' is the correct path to a directory containing a config.json file
```
I even tried setting the proxy in `proxies`: 
```config = config_class.from_pretrained(args.config_name, proxies={'http://': '<HOST>:<PORT>'})```

But same thing happens. 
Maybe there's a workaround for this?

Many thanks!