add UnexpectedAdmissionError to kube_pod_status_reason metric

[qw1mb0]

What this PR does / why we need it:
Add UnexpectedAdmissionError reason to kube_pod_status_reason metric

Which issue(s) this PR fixes:
Fixes #1114

[lilic]

thanks, can you link to where this Pod Status Reason is used in upstream k8s api, haven't been able to find it that well

[tariq1890]

I do see it being used here: https://github.com/kubernetes/kubernetes/blob/323f34858de18b862d43c40b2cced65ad8e24052/pkg/kubelet/lifecycle/predicate.go#L78

[qw1mb0]

Yes, kubelet report this reason

[qw1mb0]

In the cluster, it looks like this (kubernetes 1.16):

# kubectl -n kube-system  get pod coredns-578bdc569f-g87nk -o json | jq '.status'
{
  "message": "Pod Unexpected error while attempting to recover from admission failure: preemption: error finding a set of pods to preempt: no set of running pods found to reclaim resources: [(res: pods, q: 1), ]",
  "phase": "Failed",
  "reason": "UnexpectedAdmissionError",
  "startTime": "2020-04-19T19:30:12Z"
}

[lilic]

/lgtm

Thanks!

[k8s-ci-robot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: lilic, qw1mb0

The full list of commands accepted by this bot can be found here.

The pull request process is described here

Needs approval from an approver in each of these files:

• OWNERS [lilic]

Approvers can indicate their approval by writing /approve in a comment
Approvers can cancel approval by writing /approve cancel in a comment