`filelock.py` Error
Hi @liyucheng09, thanks for reporting.

Apparently this issue has to do with your environment setup. One question: is your data in an NFS share? Some people have reported this error when using `fcntl` to write to an NFS share... If this is the case, then it might be that your NFS just may not be set up to provide file locks. You should ask your system administrator, or try these commands in the terminal:
```shell
sudo systemctl enable rpc-statd
sudo systemctl start rpc-statd
```
## Describe the bug

It seems that the `filelock.py` went error. 

```
>>> ds=load_dataset('xsum')

^CTraceback (most recent call last):
  File "/user/HS502/yl02706/.conda/envs/lyc/lib/python3.6/site-packages/datasets/utils/filelock.py", line 402, in _acquire
    fcntl.flock(fd, fcntl.LOCK_EX | fcntl.LOCK_NB)
OSError: [Errno 37] No locks available
```

According to error log, it is OSError, but there is an `except` in the `_acquire` function.

```
    def _acquire(self):
        open_mode = os.O_WRONLY | os.O_CREAT | os.O_EXCL | os.O_TRUNC
        try:
            fd = os.open(self._lock_file, open_mode)
        except (IOError, OSError):
            pass
        else:
            self._lock_file_fd = fd
        return None
```

I don't know why it stucked rather than `pass` directly.

I am not quite familiar with filelock operation, so any help is highly appriciated.

## Steps to reproduce the bug
```python

ds = load_dataset('xsum')
```

## Expected results
A clear and concise description of the expected results.

## Actual results
```
>>> ds=load_dataset('xsum')

^CTraceback (most recent call last):
  File "/user/HS502/yl02706/.conda/envs/lyc/lib/python3.6/site-packages/datasets/utils/filelock.py", line 402, in _acquire
    fcntl.flock(fd, fcntl.LOCK_EX | fcntl.LOCK_NB)
OSError: [Errno 37] No locks available

During handling of the above exception, another exception occurred:

Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "/user/HS502/yl02706/.conda/envs/lyc/lib/python3.6/site-packages/datasets/load.py", line 818, in load_dataset
    use_auth_token=use_auth_token,
  File "/user/HS502/yl02706/.conda/envs/lyc/lib/python3.6/site-packages/datasets/load.py", line 470, in prepare_module
    with FileLock(lock_path):
  File "/user/HS502/yl02706/.conda/envs/lyc/lib/python3.6/site-packages/datasets/utils/filelock.py", line 323, in __enter__
    self.acquire()
  File "/user/HS502/yl02706/.conda/envs/lyc/lib/python3.6/site-packages/datasets/utils/filelock.py", line 272, in acquire
    self._acquire()
  File "/user/HS502/yl02706/.conda/envs/lyc/lib/python3.6/site-packages/datasets/utils/filelock.py", line 402, in _acquire
    fcntl.flock(fd, fcntl.LOCK_EX | fcntl.LOCK_NB)
KeyboardInterrupt
```

## Environment info
<!-- You can run the command `datasets-cli env` and copy-and-paste its output below. -->

- `datasets` version: 1.9.0
- Platform: Linux-4.15.0-135-generic-x86_64-with-debian-buster-sid
- Python version: 3.6.13
- PyArrow version: 4.0.1
