Update iptables_persistent_version.rb

[voreilly]

Update legacy fact from operatingsystem to os.name

Summary

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Additional Context

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• [ ] Root cause and the steps to reproduce. (If applicable)
• [ ] Thought process behind the implementation.

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Checklist

• [ ] 🟢 Spec tests.
• [ ] 🟢 Acceptance tests.
• [ ] Manually verified. (For example puppet apply)

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