Multiple Choice BERT, SWAG task, failure to test 
# 🐛 Bug

## Information

Model I am using (Bert, XLNet ...): Bert

Language I am using the model on (English, Chinese ...): English

The problem arises when using:
* [ x] the official example scripts: (give details below)
* [ x] my own modified scripts: (give details below)

The tasks I am working on is:
* [x ] an official GLUE/SQUaD task: (give the name)
* [x ] my own task or dataset: (give details below)

## To reproduce

Steps to reproduce the behavior:

1. Download SWAG dataset and put it in some directory and set the path by `export SWAG_DIR=path/to/swag/dir`
2. Copy `run_multiple_choice.py` and `utils_multiple_choice.py`
3. Run the code only for testing with the following command 
`./run_multiple_choice.py --model_type bert --task_name swag --model_name_or_path bert-base-uncased --do_lower_case --max_seq_length 80 --output_dir models_bert/swag_testing --data_dir $SWAG_DIR --do_test`

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## Expected behavior
```
Traceback (most recent call last):
  File "./run_multiple_choice.py", line 678, in <module>
    main()
  File "./run_multiple_choice.py", line 669, in main
    result = evaluate(args, model, tokenizer, prefix=prefix, test=True)
  File "./run_multiple_choice.py", line 248, in evaluate
    eval_dataset = load_and_cache_examples(args, eval_task, tokenizer, evaluate=not test, test=test)
  File "./run_multiple_choice.py", line 354, in load_and_cache_examples
    examples = processor.get_test_examples(args.data_dir)
  File "utils_multiple_choice.py", line 168, in get_test_examples
    "For swag testing, the input file does not contain a label column. It can not be tested in current code"
ValueError: For swag testing, the input file does not contain a label column. It can not be tested in current codesetting! 
```

In the code it says for testing there is no need for label column, but it doesn't work with or without it. It does not work with the default `test.csv` file (it will be called by default for testing if it is in the directory), but it also does not work with `val.csv` (has label column).

## Environment info
<!-- You can run the command `python transformers-cli env` and copy-and-paste its output below.
     Don't forget to fill out the missing fields in that output! -->
     
- `Transformers` version: current 
- Platform: Linux
- Python version: 3.7.5
- Using GPU in script?:  yes
- Using distributed or parallel set-up in script?:

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.
