CloudNodeLifecycleController: check node existence before shutdown status

[jiahuif]

What type of PR is this?
/kind bug
What this PR does / why we need it:
Currently, we check to see if the node is shutdown. If so, we never brother to move on and check if the node exists. We should check existence first because if a node no longer exists, its taints and other checks are meaningless, and, in this case, we should simply remove the node.
Which issue(s) this PR fixes:

Special notes for your reviewer:

Does this PR introduce a user-facing change?:

CloudNodeLifecycleController will check node existence status before shutdown status when monitoring nodes.

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

/cc @cheftako

[k8s-ci-robot]

Hi @jiahuif. Thanks for your PR.

I'm waiting for a kubernetes 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.

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[jiahuif]

/sig cloud-provider

[cheftako]

/ok-to-test

[jiahuif]

/assign @andrewsykim

[jiahuif]

/priority important-soon

[andrewsykim]

/approve
/lgtm

thanks @jiahuif

[k8s-ci-robot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: andrewsykim, jiahuif

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