Model Save/Load Fails for Hadoop File Server
## Environment info
- `transformers` version: 4.2.2
- Platform: Windows-10-10.0.19041-SP0
- Python version: 3.8.3
- PyTorch version (GPU?): 1.7.1 (False)
- Tensorflow version (GPU?): 2.4.0 (False)
- Using GPU in script?: No
- Using distributed or parallel set-up in script?: No

### Who can help
@n1t0, @LysandreJik @sgugger

## Information

Model I am using (Bert, XLNet ...): bert-base-uncased

The problem arises when using:
* [X] the official example scripts: 
```python
config = pipeline.get_common_model_file(model_name, Constants.CONFIG)
model = AutoModelForSequenceClassification.from_pretrained(config=config, pretrained_model_name_or_path='http://192.168.0.61:50070/webhdfs/v1/user/root/NLPEngine/models/bert-base-uncased/pytorch_model.bin?op=OPEN')
```
* [ ] my own modified scripts: 

The tasks I am working on is:
* [ ] an official GLUE/SQUaD task: (give the name)
* [X] my own task or dataset: 
A Conversational (Multi-Turn Dialog) Dataset for Task of Knowledge Selection. Dataset is raising no issues.

## To reproduce

Steps to reproduce the behavior:

1. Install Hadoop File Server
2. Setup WebHDFS to use cURL commands to load/save files on HDFS or directly use hadoop for that. Just make sure that all your servers are listed in your system's hosts configurations.
3. Place bert-base-uncased model on Hadoop (anywhere).
4. Try and access it from the code mentioned above.

## Expected behavior

The model should be loaded from the file, as it would be loaded locally or from a server that returns an E-Tag, but Hadoop is not configured / built for returning E-Tags. It first returns a temporary-redirect URL, and then from that the actual object retrieved off of one of the servers in its cluster(s). 
If I turn off the E-Tag validation in the source code, then it starts working perfectly, but as of now, its part of the source-code, and thats causing this code to crash. 
Here is the change I made to get it to work (in my copy of the library's code):

```python
File "C:\Users\rsiddiqui\Anaconda3\Lib\site-packages\transformers\file_utils.py", line 1182, in get_from_cache
etag = ''
File "C:\Users\rsiddiqui\Anaconda3\Lib\site-packages\transformers\file_utils.py", line 1187, in get_from_cache
etag = r.headers.get("X-Linked-Etag", '') or r.headers.get("ETag", '')
```

This issue has been automatically marked as stale and been closed because it has not had recent activity. Thank you for your contributions.

If you think this still needs to be addressed please comment on this thread.