Merge pull request #44588 from dmmcquay/kubeadm_skip_token_print

Automatic merge from submit-queue (batch tested with PRs 44601, 44842, 44893, 44491, 44588)

kubeadm: add flag to skip token print out

**What this PR does / why we need it**: When kubeadm init is used in an automated context, it still prints the token to standard out. When standard output ends up in a log file, it can be considered that the token is leaked there and can be compromised. This PR adds a flag you can select to not have it print out and explicitly disable this behavior.

This is a continuation from https://github.com/kubernetes/kubernetes/pull/42823 since it had to be closed.

**Which issue this PR fixes** : fixes #https://github.com/kubernetes/kubeadm/issues/160

**Special notes for your reviewer**: /cc @luxas @errordeveloper 

**Release note**:
```release-note
NONE
```

hack/verify-flags/known-flags.txt

@@ -648,6 +648,7 @@ since-time
 skip-generated-rewrite
 skip-munges
 skip-preflight-checks
+skip-token-print
 skip-unsafe
 sort-by
 source-file