Fix race condition for downloading cache when executing with multi-node
# What does this PR do ?

When downloading the tokenizer from cache with multi-node, some ranks may see that the path does not exist yet and multiple ranks will attempt to download causing errors.

**Collection**: [NLP]

# Changelog 
- Add specific line by line info of high level changes in this PR.

# Usage
* Training 5b/20b that uses the megatron cache works well with single node. ptuning 5b/20b with multi-node this error arises.


```
Traceback (most recent call last):
  File "/usr/lib/python3.8/shutil.py", line 791, in move
    os.rename(src, real_dst)
FileNotFoundError: [Errno 2] No such file or directory: '/root/.cache/torch/megatron/megatron-gpt-345m_vocab0037lvum.tmp' -> '/root/ (1).cache/torch/megatron/megatron-gpt-345m_vocab'

During handling of the above exception, another exception occurred:

Traceback (most recent call last):
  File "megatron_gpt_prompt_learning.py", line 91, in main
...
  File "/opt/NeMo/nemo/collections/nlp/modules/common/megatron/megatron_utils.py", line 211, in _download
    wget.download(url, path)
  File "/usr/local/lib/python3.8/dist-packages/wget.py", line 534, in download
    shutil.move(tmpfile, filename)
  File "/usr/lib/python3.8/shutil.py", line 811, in move
    copy_function(src, real_dst)
  File "/usr/lib/python3.8/shutil.py", line 435, in copy2
    copyfile(src, dst, follow_symlinks=follow_symlinks)
  File "/usr/lib/python3.8/shutil.py", line 264, in copyfile
    with open(src, 'rb') as fsrc, open(dst, 'wb') as fdst:
FileNotFoundError: [Errno 2] No such file or directory: '/root/ (1).cache/torch/megatron/megatron-gpt-345m_vocab'
```

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**PR Type**:
- [ ] New Feature
- [x] Bugfix
- [ ] Documentation

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# Additional Information
* Related to # (issue)
