Checkpoint conversion script breaks for meta-llama/llama-2-7b on HF

[vivianrwu]

The checkpoint conversion script breaks for https://huggingface.co/meta-llama/Llama-2-7b, because it does not have safetensor files. But when running the script, we set --from_hf=True since the checkpoint is from HF. We could include logic to check for these certain versions. https://huggingface.co/meta-llama/Llama-2-7b-hf works as expected.