Force system-node-critical daemon-sets in node group templates

[pmendelski]

What type of PR is this?

/kind bug

What this PR does / why we need it:

For --force-ds=false flag, cluster-autoscaler does not account for pending daemon-sets when creating node group templates. It sometimes leads to a cycle of node group recreations:

• User pod consuming most resources of a selected node triggers a scale-up
• System daemon-sets are started on the node
• User pod triggering the scale-up does not fit the node anymore
• Node is removed
• Back to step 1

To fix this scenario (without flipping --force-ds flag) two changes were implemented:

• Always account for preempting system-node-critical daemon-sets - those DSes will preempt other pods so it's safe to account for them in scale-up simulations. This should solve most of the problems seen in practice
• Do not pick half drained nodes as node group templates - it looks like a bug. Sometimes a half drained node is picked as a node group template leading to a situation where node is assumed to have more available resources than really assignable. This should just stabilize node count state for non system-node-critical daemon-sets.

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]

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This pull-request has been approved by: pmendelski
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[k8s-ci-robot]

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