test: improve autoscaling E2E to prevent unexpected scale operations

[comtalyst]

What type of PR is this?

/kind cleanup
/kind flake

What this PR does / why we need it:

Current autoscaling E2Es can be unreliable when trying to catch over-scaling, as it only checks once at the end.
This has resulted in a Cluster Autoscaler image that contains over-scaling issue to get through the check unnoticed.

This PR aims to increase test coverage to cover the case where there are unexpected scale operations during and after standard scaling check.

Which issue(s) this PR fixes:

Fixes #

Special notes for your reviewer:

Does this PR introduce a user-facing change?

NONE

Additional documentation e.g., KEPs (Kubernetes Enhancement Proposals), usage docs, etc.:

[k8s-ci-robot]

Hi @comtalyst. Thanks for your PR.

I'm waiting for a kubernetes-sigs member to verify that this patch is reasonable to test. If it is, they should reply with /ok-to-test on its own line. Until that is done, I will not automatically test new commits in this PR, but the usual testing commands by org members will still work. Regular contributors should join the org to skip this step.

Once the patch is verified, the new status will be reflected by the ok-to-test label.

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[lzhecheng]

/ok-to-test

[lzhecheng]

Some comments.

[lzhecheng]

@comtalyst The PR LGTM. Thank you!
The CI failure is not related to your change but a known issue for CAPZ. Please squash your PR and issue should be gone as well.

[lzhecheng]

/lgtm

[lzhecheng]

/approve

[k8s-ci-robot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: comtalyst, lzhecheng

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