tolerate discovery errors in the restmapper

[deads2k]

Found this while investigating a related problem. The restmapper can use the information it has found. It doesn't have to discard all of it.

[k8s-ci-robot]

@deads2k: Adding do-not-merge/release-note-label-needed because the release note process has not been followed.

One of the following labels is required "release-note", "release-note-action-required", or "release-note-none".
Please see: https://github.com/kubernetes/community/blob/master/contributors/devel/pull-requests.md#write-release-notes-if-needed.

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[deads2k]

/retest

[deads2k]

@p0lyn0mial you were in here long ago mind taking a look

//asssign p0lyn0mial

[shiywang]

/lgtm

[deads2k]

/approve no-issue

[k8s-github-robot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: deads2k, shiywang

Associated issue requirement bypassed by: deads2k

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

Needs approval from an approver in each of these OWNERS Files:

• pkg/kubectl/OWNERS [deads2k]

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[p0lyn0mial]

sorry for the delay, looks good to me.

[k8s-github-robot]

/test all [submit-queue is verifying that this PR is safe to merge]

[k8s-github-robot]

Automatic merge from submit-queue. If you want to cherry-pick this change to another branch, please follow the instructions here.