order caffe2 ubuntu configs contiguously (#17427)
Summary:
This involves another purely cosmetic (ordering) change to the `config.yml` to facilitate simpler logic.
Other changes:
* add some review feedback as comments
* exit with nonzero status on config.yml mismatch
* produce a diagram for pytorch builds
Pull Request resolved: https://github.com/pytorch/pytorch/pull/17427
Differential Revision: D14197618
Pulled By: kostmo
fbshipit-source-id: 267439d3aa4c0a80801adcde2fa714268865900e
