Ensure added taints are present on the node in the snapshot

[norbertcyran]

What type of PR is this?

/kind bug

What this PR does / why we need it:

There's an inconsistency in AddTaints behavior. AddTaints makes a copy of the node, the taints are added to the spec of the copy, but not to the original spec. Meanwhile HasTaints checks if the taint is present in the spec of the node. Therefore, the changes made by AddTaints won't be present in the snapshot until the next autoscaler loop.

This PR ensures that the new taints are also added to the spec of the node in the snapshot. I also had to fix static autoscaler test, as it was configured improperly. As k8s API client was mocked, in the previous implementation marking the node as deleted was no-op in this test. Therefore, the unschedulable pod was scheduled to the removed node, which would not happen in the real scenario, as the node would refresh its taints in the beginning of the autoscaler loop. As AddTaints now adds taints also to the node spec, that unschedulable pod was triggering scale up, which wasn't expected by the mock. As scale up logic has already been tested in previous run, the fix was to simply remove that pod from the unschedulable pods list. Couple of other static autoscaler test cases also failed because they depended on this bug

Does this PR introduce a user-facing change?

NONE

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

[k8s-ci-robot]

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[k8s-ci-robot]

Hi @norbertcyran. Thanks for your PR.

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