Add raw to file names

[bobhenkel]

The gcp images contain the word raw in the file names. This caused a error when following the online guide.

Pull Request

What? (description)

Online docs reference gcp-amd64.tar.gz but the actual final name is gcp-amd64.raw.tar.gz

Why? (reasoning)

When I followed the instructions they failed because of this file name issue.

Acceptance

Please use the following checklist:

• [ NA] you linked an issue (if applicable)
• [ NA] you included tests (if applicable)
• [ ] you ran conformance (make conformance)
• [ ] you formatted your code (make fmt)
• [ ] you linted your code (make lint)
• [ ] you generated documentation (make docs)
• [ ] you ran unit-tests (make unit-tests)

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