kubeadm: Avoid logging token in RunDeleteTokens

[mlevesquedion]

What type of PR is this?
/kind bug

What this PR does / why we need it:
This PR fixes a (small) vulnerability in kubeadm. I have reported the vulnerability to HackerOne and they have informed me that based on the high attack complexity and low severity, they think this can be reported and fixed publicly. Details are in this issue: kubernetes/kubeadm#2287

Does this PR introduce a user-facing change?:

NONE

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[k8s-ci-robot]

Hi @mlevesquedion. Thanks for your PR.

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[SataQiu]

Thanks @mlevesquedion
/ok-to-test

[neolit123]

here we can assume if the token pattern is invalid, the token is invalid. so printing it here as part of the error can only be problematic if a good token is part of the message - e.g. valid-tokenfoo, where if foo is removed one can get the token.

in any case this change is fine.

[neolit123]

thanks for the PR
/lgtm
/approve
/priority backlog

[k8s-ci-robot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: mlevesquedion, neolit123

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[neolit123]

/milestone v1.20