Add more verbose logging to IsEvictable checks

[damemi]

This makes the IsEvictable check more verbose at logLevel=4, but breaking each check into its own conditional and logging errors for each one, finally outputting the full list if the pod does not also have the "evictable" annotation.

This gives output like this:

I0529 16:14:06.044444       1 pods.go:60] Pod dedicated-nodes-vkr8s in namespace test-ns is not evictable: Pod lacks an eviction annotation and fails the following checks: [pod is critical, pod does not have any ownerrefs]

[k8s-ci-robot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: damemi

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[damemi]

/hold
I haven't personally tested this yet to see what the error output looks like. If someone else gets to it before I do and it looks fine anyone can feel free to remove the hold

[seanmalloy]

/kind cleanup

[seanmalloy]

@damemi I think it would be good to note in the Pod Evictions section of the README that using log level 4 will log the reason descheduler is not evicting a pod. I believe this would reduce the number of questions end users have about why pods are not being evicted.

[damemi]

@seanmalloy good idea, updated

[seanmalloy]

/lgtm

The hold can be removed once someone has verified what the log output actually looks like.

[damemi]

Finally got to test this and the output looks good to me:

I0529 16:14:06.044444       1 pods.go:60] Pod dedicated-nodes-vkr8s in namespace test-ns is not evictable: Pod lacks an eviction annotation and fails the following checks: [pod is critical, pod does not have any ownerrefs]

Note that this does log for a lot of pods (every pod that's not evictable) so to really debug it you need to grep the logs, but I think that's reasonable for v=4

/hold cancel

[ingvagabund]

/retest

[ingvagabund]

/test pull-descheduler-verify