✨ Update to Kubernetes 1.12.3

[jimmidyson]

As requested in #221 (comment)

This has no breaking changes, only changes to dependencies and internal changes to work with the new version.

[jimmidyson]

Wait - I just noticed there are no differences in vendored files... so what to do here? @DirectXMan12? It's a shame we have to reference a specific tagged version of Kubernetes (e.g. kubernetes-1.12.3) rather than a branch (e.g. release-1.12). How do you feel about referencing the branch instead?

/assign @DirectXMan12

[jimmidyson]

@DirectXMan12 @mengqiy Any time to review?

[mengqiy]

We generally pin all the k8s dep to a released version instead of a branch. We upgrade the k8s dep about once per quarter, so these 2 approaches don't have much differences for us.

No breaking changes
/lgtm

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[jimmidyson]

OK thanks for explaining @mengqiy. This PR follows that convention and pins to released versions. Would be good to merge :)

[jimmidyson]

I want to update controller-tools but need a tag to reference there. Can someone do that please?

[mengqiy]

I want to update controller-tools but need a tag to reference there. Can someone do that please?

There are some changes we want to make about the metric support before tagging a new release.
Please expect a new release to happen this Wednesday or Thursday.