add logging to make the saving action visible (#19042)
Summary:
Pull Request resolved: https://github.com/pytorch/pytorch/pull/19042
show the model saving step in the log.
Reviewed By: kennyhorror
Differential Revision: D14809385
fbshipit-source-id: c7a1e50ff92bb45b16b1c501d9325b304b07fbd3
