reduce plan generation log spam (#70880)
Summary:
Pull Request resolved: https://github.com/pytorch/pytorch/pull/70880
Change loglevel to `debug` in caffe2 `optimizer.py` for logging rowwise Adagrad engine.
Test Plan: CI + sandcastle
Reviewed By: boryiingsu
Differential Revision: D33439337
fbshipit-source-id: b158249b8df771c0ec8b642210ede39972929b00
