Summary:
In ```cmp_with_scann.py```, we will save npy file for base and query vector file and gt file. However, we will only do this while the lib is faiss, if we directly run this script with scann lib it will complain that file does not exsit.
Therefore, the code should be refactored to save npy file from the beginning so that nothing will go wrong.
Pull Request resolved: https://github.com/facebookresearch/faiss/pull/2573
Reviewed By: mdouze
Differential Revision: D42338435
Pulled By: algoriddle
fbshipit-source-id: 9227f95e1ff79f5329f6206a0cb7ca169185fdb3