Add parameter verification of specified cloud node.

[yanyhui]

What type of PR is this?

Uncomment only one /kind <> line, hit enter to put that in a new line, and remove leading whitespace from that line:
/kind bug
/kind documentation
/kind enhancement
/kind good-first-issue
/kind feature
/kind question
/kind design
/sig ai
/sig iot
/sig network
/sig storage
/sig storage

/kind bug

What this PR does / why we need it:

This is the solution
no cloud node is specified when executing the yurtctl convert command, but the program does not report an error.

Which issue(s) this PR fixes:

Fixes #335

Special notes for your reviewer:

Does this PR introduce a user-facing change?

other Note

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In response to this:

What type of PR is this?

Uncomment only one /kind <> line, hit enter to put that in a new line, and remove leading whitespace from that line:
/kind bug
/kind documentation
/kind enhancement
/kind good-first-issue
/kind feature
/kind question
/kind design
/sig ai
/sig iot
/sig network
/sig storage
/sig storage

What this PR does / why we need it:

Which issue(s) this PR fixes:

Fixes #335

Special notes for your reviewer:

Does this PR introduce a user-facing change?

other Note

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[kadisi]

/kind bug

[rambohe-ch]

/assign @Peeknut

[Peeknut]

lgtm

[Fei-Guo]

/approve
/lgtm

[openyurt-bot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: Fei-Guo, yanyhui

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