WIP: Switchover to dep / K8s stuff

Disclaimer: I do not intend to get this specific patchset merged (for pretty obvious reasons), that's why there is no MR template.

This does a ton of dependency work including a switchover to dep, new Kubernetes API versions, ... It's based on merging/cherrypicking different branches of @martell, @nolith and gitlab-runner master and a LOT of trial and error and chasing Github issues. Sadly all this stuff is insanely hard to decouple.

The interesting parts are that the Gopkg file installs perfectly without a vendor folder (dep ensure is all that's needed) and contains all updates from !753 (closed) and support for Kubernetes API up to 1.7 instead of the previous 1.3. Also has no dependency conflicts.

Then there is an experimental fix for #2718 (closed) and #2742 (closed) in there too, that was the primary reason for this whole thing.

So obviously we can't just go ahead and merge this whole mess (also there are obviously concerns with switching vendoring tools as discussed in !753 (closed)) but all the parts are now here, the question is what do we do with them.

Tagging potentially interested people (from the MRs and issues): @tmaczukin @ayufan @urbaniak