Kubeadm: Refactor token.go flag names into const

[fabriziopandini]

Flag names in token.go should be refactored into constants.

e.g. flag name token defined here
https://github.com/kubernetes/kubernetes/blob/7c112762b0df87f3a1772f3bbede7fe9185fa249/cmd/kubeadm/app/cmd/options/token.go#L48

Should be refactored into a constant defined into constant.go

The same apply for token-ttl, usages, groups, description flags

[MalloZup]

ciao @fabriziopandini i can take this one but i will start looking at it after new year :fireworks: :dragon_face: :dragon_face: :dragon: :white_flower: :fireworks:

[fabriziopandini]

/assign @MalloZup

[k8s-ci-robot]

@fabriziopandini: GitHub didn't allow me to assign the following users: MalloZup.

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In response to this:

/assign @MalloZup

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[Zyqsempai]

I can make it today;) Of course, If @MalloZup doesn't mind)

[fabriziopandini]

@Zyqsempai please sync with @MalloZup; this is not urgent

[Zyqsempai]

@fabriziopandini Sure.

[MalloZup]

@Zyqsempai i don't mind if you tackle this issue.

If you tackle this, reference your PR or PRs to this Issue so i know what you are working on.

From my part i will relook on this issue after the 3 January, so if you wish to solve it before feel free! :)
( if isn't fixed with a PR i will look at it)

For me is just for learning more the step by step internals of kubeadm, so is fine for me to pick another issue the next time :sun_with_face: .

[Zyqsempai]

@MalloZup thanks, I will track my activity here.

[Zyqsempai]

PR is opened, waiting for some comments or approval.

[bart0sh]

/cc @fabriziopandini

[Zyqsempai]

Done, merged, we can close the issue!!

[yagonobre]

Thanks @Zyqsempai
/close

[k8s-ci-robot]

@yagonobre: Closing this issue.

In response to this:

Thanks @Zyqsempai
/close

Instructions for interacting with me using PR comments are available here. If you have questions or suggestions related to my behavior, please file an issue against the kubernetes/test-infra repository.