[CI][treehug] Disable xenial_py2.7 tests due to mypy min version py3.5
Summary: Pull Request resolved: https://github.com/pytorch/pytorch/pull/33159
Test Plan: Imported from OSS
Differential Revision: D19822400
Pulled By: IvanKobzarev
fbshipit-source-id: 8e7b561e6a6181ec1f9b6f56a539ddcb538b3858
