Update developer tooling to Kubernetes 1.15

[roberthbailey]

What type of PR is this?

Uncomment only one /kind <> line, hit enter to put that in a new line, and remove leading whitespace from that line:

/kind breaking

/kind bug
/kind cleanup
/kind documentation
/kind feature
/kind hotfix

What this PR does / Why we need it:

Which issue(s) this PR fixes:

First part of #1478

Special notes for your reviewer:

[agones-bot]

Build Succeeded 👏

Build Id: ed4da469-c9bd-4e55-8453-da3326bdfa94

The following development artifacts have been built, and will exist for the next 30 days:

• image: gcr.io/agones-images/agones-controller:1.6.0-fcb3ef4
• image: gcr.io/agones-images/agones-sdk:1.6.0-fcb3ef4
• image: gcr.io/agones-images/agones-ping:1.6.0-fcb3ef4
• Linux C++ SDK (build): agonessdk-1.6.0-fcb3ef4-linux-arch_64.tar.gz
• SDK Server: agonessdk-server-1.6.0-fcb3ef4.zip

A preview of the website (the last 30 builds are retained):

• https://fcb3ef4-dot-preview-dot-agones-images.appspot.com/

To install this version:

• git fetch https://github.com/GoogleCloudPlatform/agones.git pull/1486/head:pr_1486 && git checkout pr_1486
• helm install ./install/helm/agones --namespace agones-system --name agones --set agones.image.tag=1.6.0-fcb3ef4

[markmandel]

👍

[google-oss-robot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: markmandel, roberthbailey

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