finetune.py: error: unrecognized arguments
### Who can help

 examples/distillation: @VictorSanh
 examples/seq2seq: @sshleifer

## Information

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

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

The tasks I am working on is:
* [ ] 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. Try running seq2seq/finetune.sh with data_dir or output_dir with escaped spaces in it
2. You'll get a `finetune.py: error: unrecognized arguments`

This is bad because Google Drive mounts at `/content/drive/My Drive/` in Colab and thus the example scripts won't work if saving or reading from Drive.

I've created a [Colab Notebook](https://colab.research.google.com/drive/1N-8m9FC9GbAywVJZAgSBkLqe24SPRfl8?usp=sharing) with repro.

The fix I've found is to change:
```
python finetune.py \
    --learning_rate=3e-5 \
    --fp16 \
    --gpus 1 \
    --do_train \
    --do_predict \
    --n_val 1000 \
    --val_check_interval 0.1 \
    $@
```
to 
```
python finetune.py \
    --learning_rate=3e-5 \
    --fp16 \
    --gpus 1 \
    --do_train \
    --do_predict \
    --n_val 1000 \
    --val_check_interval 0.1 \
    "$@"
```
