Upgrade kubectl for e2e tests

[markmandel]

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:

One of the pieces for upgrade to Kubernetes 1.15

Which issue(s) this PR fixes:

Work on #1478

Special notes for your reviewer:

I was going to switch to wget, but this ticket indicates that this is an intermittent network error. I'm hoping that pointing to a newer version of Kubectl solves this.

[google-oss-robot]

[APPROVALNOTIFIER] This PR is APPROVED

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

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• OWNERS [markmandel]

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[agones-bot]

Build Succeeded 👏

Build Id: 400f0bfb-2d87-441d-b3f7-a1a62a872d4d

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-bf47876
• image: gcr.io/agones-images/agones-sdk:1.6.0-bf47876
• image: gcr.io/agones-images/agones-ping:1.6.0-bf47876
• Linux C++ SDK (build): agonessdk-1.6.0-bf47876-linux-arch_64.tar.gz
• SDK Server: agonessdk-server-1.6.0-bf47876.zip

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

• https://bf47876-dot-preview-dot-agones-images.appspot.com/

To install this version:

• git fetch https://github.com/GoogleCloudPlatform/agones.git pull/1550/head:pr_1550 && git checkout pr_1550
• helm install ./install/helm/agones --namespace agones-system --name agones --set agones.image.tag=1.6.0-bf47876

[google-oss-robot]

New changes are detected. LGTM label has been removed.

[agones-bot]

Build Succeeded 👏

Build Id: 7940c9d5-830d-40a8-a074-8461279f7cfc

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

• image: gcr.io/agones-images/agones-controller:1.6.0-6600fec
• image: gcr.io/agones-images/agones-sdk:1.6.0-6600fec
• image: gcr.io/agones-images/agones-ping:1.6.0-6600fec
• Linux C++ SDK (build): agonessdk-1.6.0-6600fec-linux-arch_64.tar.gz
• SDK Server: agonessdk-server-1.6.0-6600fec.zip

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

• https://6600fec-dot-preview-dot-agones-images.appspot.com/

To install this version:

• git fetch https://github.com/GoogleCloudPlatform/agones.git pull/1550/head:pr_1550 && git checkout pr_1550
• helm install ./install/helm/agones --namespace agones-system --name agones --set agones.image.tag=1.6.0-6600fec