Fix run_glue evaluation when model has a label correspondence
# What does this PR do?

The `run_glue` script uses the correspondence id to label stored in a given model but when using
```
AutoModelForSequenceClassication.from_pretrained(xxx, num_labels=x)
```
that correspondence is reset. This PR fixes that, along with a few other bugs in the script. To confirm MNLI evaluation does take the correspondence in a model config
```bash
python examples/text-classification/run_glue.py --model_name_or_path roberta-large-mnli --task_name mnli --max_seq_length 128 --output_dir ~/tmp/test-mnli --do_eval
```
gices 90.6%/90.1% accuracy (matched/mismatched) after this PR, vs 4.28%/4.86% accuracy on current master.