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Fix kubeadm command related typos, punctuation and capitalization
**What this PR does / why we need it**:
This PR deals with a numerous fixes of small punctuation, capitalization and wording typos in the kubeadm/app/cmd namespace. It cleans the output shown to the user in stdout.
**Which issue this PR fixes** *(optional, in `fixes #<issue number>(, fixes #<issue_number>, ...)` format, will close that issue when PR gets merged)*: fixes #
/approve no-issue
**Special notes for your reviewer**:
I can easily amend, remove or squash certain changes, so if you think there is a need for that - please, let me know.
Lubomir I. Ivanov (VMWare)
2124c73d60