Upgrade kubectl to 1.20 in dev tooling.

[roberthbailey]

What type of PR is this?

Uncomment only one /kind <> line, press 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:
Work on #2186

Special notes for your reviewer:

[agones-bot]

Build Succeeded 👏

Build Id: cdc674a2-7c7f-4c1f-9d97-2bf22c06d4cc

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

• image: gcr.io/agones-images/agones-controller:1.17.0-be6e67b
• image: gcr.io/agones-images/agones-ping:1.17.0-be6e67b
• Linux C++ SDK (build): agonessdk-1.17.0-be6e67b-linux-arch_64.tar.gz
• SDK Server: agonessdk-server-1.17.0-be6e67b.zip

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

• https://be6e67b-dot-preview-dot-agones-images.appspot.com/

To install this version:

• git fetch https://github.com/googleforgames/agones.git pull/2189/head:pr_2189 && git checkout pr_2189
• helm install ./install/helm/agones --namespace agones-system --name agones --set agones.image.tag=1.17.0-be6e67b

[agones-bot]

Build Succeeded 👏

Build Id: fc69bbbb-b669-44d5-ad0b-7ad24bea729b

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

• image: gcr.io/agones-images/agones-controller:1.17.0-6892a09
• image: gcr.io/agones-images/agones-ping:1.17.0-6892a09
• Linux C++ SDK (build): agonessdk-1.17.0-6892a09-linux-arch_64.tar.gz
• SDK Server: agonessdk-server-1.17.0-6892a09.zip

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

• https://6892a09-dot-preview-dot-agones-images.appspot.com/

To install this version:

• git fetch https://github.com/googleforgames/agones.git pull/2189/head:pr_2189 && git checkout pr_2189
• helm install ./install/helm/agones --namespace agones-system --name agones --set agones.image.tag=1.17.0-6892a09

[google-oss-robot]

[APPROVALNOTIFIER] This PR is APPROVED

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

The full list of commands accepted by this bot can be found here.

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Needs approval from an approver in each of these files:

• OWNERS [markmandel,roberthbailey]

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