fix: check if NodeExternalIP is empty to fallback to NodeInternalIP

[aarnaud]

Check if NodeExternalIP is empty to use NodeInternalIP with private GKE cluster

[googlebot]

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[agones-bot]

Build Failed 😱

Build Id: b9fbb768-5fc7-42ba-9c92-afadb3489e6d

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[googlebot]

CLAs look good, thanks!

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[agones-bot]

Build Succeeded 👏

Build Id: 9b2dd483-3a41-4e5e-9934-f043ad092d8f

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

• image: gcr.io/agones-images/agones-controller:0.11.0-f65939e
• image: gcr.io/agones-images/agones-sdk:0.11.0-f65939e
• image: gcr.io/agones-images/agones-ping:0.11.0-f65939e
• Linux C++ SDK (build): agonessdk-0.11.0-f65939e-linux-arch_64.tar.gz
• SDK Server: agonessdk-server-0.11.0-f65939e.zip

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

• https://f65939e-dot-preview-dot-agones-images.appspot.com/

To install this version:

• git fetch https://github.com/GoogleCloudPlatform/agones.git pull/828/head:pr_828 && git checkout pr_828
• helm install install/helm/agones --namespace agones-system --name agones --set agones.image.tag=0.11.0-f65939e

[markmandel]

Nice! 😻