tree: import manifests, configs, and jobs

[jlebon]

This commit includes all the juicy bits needed to set up a Jenkins instance in which to run our upstream CI. Lots going on here, but some highlights:

• the configs are fully declarative; there's nothing more to set up once Jenkins is up (well, almost... working on that)
• we use the same Jenkins build config as the FCOS pipeline to match its environment
• we set up GitHub OAuth for authentication
• the job creation system is kept flexible enough that it's not just for running GitHub PR tests, any arbitrary job can be added; one simply needs to add the Jenkinsfile to jobs/ (in fact, I'd like to experiment with the same setup for the FCOS pipeline itself)

Anyway, there's more tweaks needed to get this where we want, but I think it's in a good enough state to get it in.

[jlebon]

Requires: https://github.com/coreos/fedora-coreos-pipeline/pull/197

[jlebon]

Once this is merged, I'll transfer the repo over to the coreos/ org.