Add throwing error when specifying unsupported os in Vagrant

[THUzxj]

What type of PR is this?

/kind feature

What this PR does / why we need it:

Tell the user which OSes are supported, or they can only see an error thrown by SUPPORTED_OS[$os][:box] and make effort to locate the error.

Which issue(s) this PR fixes:

Fixes #

Special notes for your reviewer:

Does this PR introduce a user-facing change?:

Throw an error when specifying unsupported os in Vagrant

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• ✅ login: THUzxj / name: Xingjian Zhang (67669f7)

[k8s-ci-robot]

Hi @THUzxj. Thanks for your PR.

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[yankay]

Thanks @THUzxj

/lgtm
/ok-to-test

[oomichi]

/approve

[k8s-ci-robot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: oomichi, THUzxj

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