test: HPA/cluster-autoscaler fixes so we don't scale up too many pods

[jackfrancis]

Reason for Change:

It seems that due to this issue our increase of node pools has revealed a bug in HPA, where it doesn't scale down if pods are Pending:

kubernetes/kubernetes#85506

This PR only calculates cluster-autoscaler-engaged node pools when determining how to configure HPA for scale up, so that there aren't Pending pods when we stop load.

Issue Fixed:

Requirements:

• uses conventional commit messages
• includes documentation
• adds unit tests
• tested upgrade from previous version

Notes:

[acs-bot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: jackfrancis

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