Tests update: Added require statements to gameserversets package

[akremsa]

What type of PR is this?

/kind bug
/kind cleanup

What this PR does / Why we need it:
Use require package to abort tests in order to avoid nil pointer exceptions.

[agones-bot]

Build Failed 😱

Build Id: faf5c34b-a6a5-4946-93cb-04b946aca04d

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[agones-bot]

Build Succeeded 👏

Build Id: 97d3c474-8158-4e29-a7e5-82d44f1c6ed3

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

• image: gcr.io/agones-images/agones-controller:1.8.0-1efe2ec
• image: gcr.io/agones-images/agones-sdk:1.8.0-1efe2ec
• image: gcr.io/agones-images/agones-ping:1.8.0-1efe2ec
• Linux C++ SDK (build): agonessdk-1.8.0-1efe2ec-linux-arch_64.tar.gz
• SDK Server: agonessdk-server-1.8.0-1efe2ec.zip

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

• https://1efe2ec-dot-preview-dot-agones-images.appspot.com/

To install this version:

• git fetch https://github.com/googleforgames/agones.git pull/1696/head:pr_1696 && git checkout pr_1696
• helm install ./install/helm/agones --namespace agones-system --name agones --set agones.image.tag=1.8.0-1efe2ec

[google-oss-robot]

[APPROVALNOTIFIER] This PR is APPROVED

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

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[google-oss-robot]

New changes are detected. LGTM label has been removed.

[agones-bot]

Build Succeeded 👏

Build Id: 03af7d2e-3478-4ba5-9577-2d9f8d3b71a2

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

• image: gcr.io/agones-images/agones-controller:1.8.0-d904f2a
• image: gcr.io/agones-images/agones-sdk:1.8.0-d904f2a
• image: gcr.io/agones-images/agones-ping:1.8.0-d904f2a
• Linux C++ SDK (build): agonessdk-1.8.0-d904f2a-linux-arch_64.tar.gz
• SDK Server: agonessdk-server-1.8.0-d904f2a.zip

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

• https://d904f2a-dot-preview-dot-agones-images.appspot.com/

To install this version:

• git fetch https://github.com/googleforgames/agones.git pull/1696/head:pr_1696 && git checkout pr_1696
• helm install ./install/helm/agones --namespace agones-system --name agones --set agones.image.tag=1.8.0-d904f2a