Add rocky linux support to GetOSVersion

[sudheernv]

Issue: Node Problem Detector fails to come up on rocky linux OS.

Error Log: Failed to retrieve OS version: Unsupported ID in /etc/os-release: "rocky"

[linux-foundation-easycla[bot]]

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• :white_check_mark: login: sudheernv (7ee2a4dcda5387d9e20d8eafb49c117c3a8c6770)

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[k8s-ci-robot]

Hi @sudheernv. Thanks for your PR.

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[mmiranda96]

Your new unit test is failing.

[sudheernv]

Your new unit test is failing.

Sorry @mmiranda96. Yesterday, I inadvertently omitted pushing the commit that contained the correct expected string for the newly introduced test case. Pushed new commit with necessary fix now.

-- expectedOSVersion: "8.5 (Green Obsidian)", ++ expectedOSVersion: "rocky 8.5 (Green Obsidian)",

[hakman]

/cc @wangzhen127 @vteratipally

[k8s-ci-robot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: sudheernv, vteratipally

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