Upgrades and slaves

Discuss me. Merge me.

We've generally discussed all the goals already, so commit messages are self-explanatory.

Technically, I don't think bugfix_docker_resolvconf should be in here because it's a bug fix dependent on both jenkins and docker, and this boshrelease should be relatively agnostic to that combo. A more appropriate place would be in a labs-operations boshrelease of internal packages/jobs, or a separate bosh release; former nonexistent, latter inconvenient.
Labelling where the blobs come from is super helpful.  :+1: