[CircleCI] s/ubuntu-1604:202007-01/ubuntu-2004:202104-01/ (#58308)
Summary:
Switch to latest ubuntu supported by CircleCI, according to https://circleci.com/docs/2.0/configuration-reference/#machine
Also upgrade awscli from 1.x to 2.x, which requires replacing aws ecr get-login with awc ecr get-login-password, per https://docs.aws.amazon.com/cli/latest/userguide/cliv2-migration.html#cliv2-migration-ecr-get-login
Pull Request resolved: https://github.com/pytorch/pytorch/pull/58308
Reviewed By: walterddr
Differential Revision: D28446659
Pulled By: malfet
fbshipit-source-id: 260f795dce83b3d191d8e3fa629c77c1b9fae36c
