Improved fleetautoscalers - controller unit tests

[akremsa]

What type of PR is this?

/kind cleanup

What this PR does / Why we need it:
Added missing unit tests, refactored some old ones.

Special notes for your reviewer:
Before:

After:

[agones-bot]

Build Succeeded 👏

Build Id: 2bfaab00-efc9-466e-ba26-3b424bf8ad68

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

• image: gcr.io/agones-images/agones-controller:1.6.0-7e9e2e0
• image: gcr.io/agones-images/agones-sdk:1.6.0-7e9e2e0
• image: gcr.io/agones-images/agones-ping:1.6.0-7e9e2e0
• Linux C++ SDK (build): agonessdk-1.6.0-7e9e2e0-linux-arch_64.tar.gz
• SDK Server: agonessdk-server-1.6.0-7e9e2e0.zip

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

• https://7e9e2e0-dot-preview-dot-agones-images.appspot.com/

To install this version:

• git fetch https://github.com/GoogleCloudPlatform/agones.git pull/1515/head:pr_1515 && git checkout pr_1515
• helm install ./install/helm/agones --namespace agones-system --name agones --set agones.image.tag=1.6.0-7e9e2e0

[markmandel]

Nice!

[google-oss-robot]

[APPROVALNOTIFIER] This PR is APPROVED

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

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• OWNERS [markmandel]

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