Cherry-pick #18514 to 7.x: Fix fields in kvm status metricset

[jsoriano]

Cherry-pick of PR #18514 to 7.x branch. Original message:

What does this PR do?

• Add kvm.id and kvm.name fields at the module level, as used by the new status metricset.
• Remove one redundant level in the status field.
• Add a TestData.

Why is it important?

Fix fields in new status metricset.

Checklist

• My code follows the style guidelines of this project
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
• I have made corresponding change to the default configuration files
• I have added tests that prove my fix is effective or that my feature works
• I have added an entry in CHANGELOG.next.asciidoc or CHANGELOG-developer.next.asciidoc.

Related issues

• Related to Add domain state to kvm module #17673

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[elasticmachine]

💚 Build Succeeded

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Build stats

• Build Cause: [Pull request Cherry-pick #18514 to 7.x: Fix fields in kvm status metricset #18565 opened]

• Start Time: 2020-05-15T09:36:31.268+0000

• Duration: 69 min 32 sec (4111617)

Test stats 🧪

Test	Results
Failed	0
Passed	2325
Skipped	563
Total	2888