Add suite of official CI scripts
I'm done with fixes and ready for a re-review. Hi @angerson  It seems auto-merge is not happening but the changes are merged into master now, so we can close this. Thank you for the PR.
This PR creates a suite of tidied CI scripts, extracted from previously-private TensorFlow source code within Google. It is still a work-in-progress, and as such is not yet documented. I'll be creating internal CI jobs to experiment with these, but I first need to have them merged.
