"File name too long" error for file locks
Hi @lmmx,

Thanks for providing the result of the command. I've opened a PR, and it would be great if you could verify that the fix works on your system. To install the version of the datasets with the fix, please run the following command:
```
pip install git+https://github.com/huggingface/datasets.git@fix-2924
```

Btw, I saw your PR, and I appreciate your effort. However, my approach is a bit simpler for the end-user, so that's why I decided to fix the issue myself.
## Describe the bug

Getting the following error when calling `load_dataset("gar1t/test")`:

```
OSError: [Errno 36] File name too long: '<user>/.cache/huggingface/datasets/_home_garrett_.cache_huggingface_datasets_csv_test-7c856aea083a7043_0.0.0_9144e0a4e8435090117cea53e6c7537173ef2304525df4a077c435d8ee7828ff.incomplete.lock'
```

## Steps to reproduce the bug

Where the user cache dir (e.g. `~/.cache`) is on a file system that limits filenames to 255 chars (e.g. ext4):

```python
from datasets import load_dataset
load_dataset("gar1t/test")
```

## Expected results

Expect the function to return without an error.

## Actual results

```
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "<python_venv>/lib/python3.9/site-packages/datasets/load.py", line 1112, in load_dataset
    builder_instance.download_and_prepare(
  File "<python_venv>/lib/python3.9/site-packages/datasets/builder.py", line 644, in download_and_prepare
    self._save_info()
  File "<python_venv>/lib/python3.9/site-packages/datasets/builder.py", line 765, in _save_info
    with FileLock(lock_path):
  File "<python_venv>/lib/python3.9/site-packages/datasets/utils/filelock.py", line 323, in __enter__
    self.acquire()
  File "<python_venv>/lib/python3.9/site-packages/datasets/utils/filelock.py", line 272, in acquire
    self._acquire()
  File "<python_venv>/lib/python3.9/site-packages/datasets/utils/filelock.py", line 403, in _acquire
    fd = os.open(self._lock_file, open_mode)
OSError: [Errno 36] File name too long: '<user>/.cache/huggingface/datasets/_home_garrett_.cache_huggingface_datasets_csv_test-7c856aea083a7043_0.0.0_9144e0a4e8435090117cea53e6c7537173ef2304525df4a077c435d8ee7828ff.incomplete.lock'
```

## Environment info

- `datasets` version: 1.12.1
- Platform: Linux-5.11.0-27-generic-x86_64-with-glibc2.31
- Python version: 3.9.7
- PyArrow version: 5.0.0

"File name too long" error for file locks 
 ## Describe the bug

Getting the following error when calling `load_dataset("gar1t/test")`:

```
OSError: [Errno 36] File name too long: '<user>/.cache/huggingface/datasets/_home_garrett_.cache_huggingface_datasets_csv_test-7c856aea083a7043_0.0.0_9144e0a4e8435090117cea53e6c7537173ef2304525df4a077c435d8ee7828ff.incomplete.lock'
```

## Steps to reproduce the bug

Where the user cache dir (e.g. `~/.cache`) is on a file system that limits filenames to 255 chars (e.g. ext4):

```python
from datasets import load_dataset
load_dataset("gar1t/test")
```

## Expected results

Expect the function to return without an error.

## Actual results

```
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "<python_venv>/lib/python3.9/site-packages/datasets/load.py", line 1112, in load_dataset
    builder_instance.download_and_prepare(
  File "<python_venv>/lib/python3.9/site-packages/datasets/builder.py", line 644, in download_and_prepare
    self._save_info()
  File "<python_venv>/lib/python3.9/site-packages/datasets/builder.py", line 765, in _save_info
    with FileLock(lock_path):
  File "<python_venv>/lib/python3.9/site-packages/datasets/utils/filelock.py", line 323, in __enter__
    self.acquire()
  File "<python_venv>/lib/python3.9/site-packages/datasets/utils/filelock.py", line 272, in acquire
    self._acquire()
  File "<python_venv>/lib/python3.9/site-packages/datasets/utils/filelock.py", line 403, in _acquire
    fd = os.open(self._lock_file, open_mode)
OSError: [Errno 36] File name too long: '<user>/.cache/huggingface/datasets/_home_garrett_.cache_huggingface_datasets_csv_test-7c856aea083a7043_0.0.0_9144e0a4e8435090117cea53e6c7537173ef2304525df4a077c435d8ee7828ff.incomplete.lock'
```

## Environment info

- `datasets` version: 1.12.1
- Platform: Linux-5.11.0-27-generic-x86_64-with-glibc2.31
- Python version: 3.9.7
- PyArrow version: 5.0.0
 
 Hi @lmmx,

Thanks for providing the result of the command. I've opened a PR, and it would be great if you could verify that the fix works on your system. To install the version of the datasets with the fix, please run the following command:
```
pip install git+https://github.com/huggingface/datasets.git@fix-2924
```

Btw, I saw your PR, and I appreciate your effort. However, my approach is a bit simpler for the end-user, so that's why I decided to fix the issue myself.