Workaround python2.7 find_module limitation / explicitly close file (#20782)
Summary:
fix #20781 #20757
hmm I don't know an easy way to add a test to make sure it runs against a package installed as .egg. But i tested it locally with torchvision.
Pull Request resolved: https://github.com/pytorch/pytorch/pull/20782
Differential Revision: D15443600
Pulled By: ailzhang
fbshipit-source-id: 285eb0d9a44d6edb8e93618fa293f4feb431d2ae
