Do not skip PreviewOnly test in -short mode

[t0yv0]

What happened?

Currently PreviewOnly upgrade tests skip themselves in -short mode however this is not ideal as it overloads another emerging convention we have in places like azure-native. Specifically, -short is used to skip very long running integration tests (think 20 minutes) but allow faster running integration tests (think 1 minute) to pass through. PreviewOnly tests are more in the 1 minute range so they should be permitted through -short to be conventional here.

Instead if #14 is adopted skip these tests when creds are not available, if the user opts into running in creds-free mode.

Example

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Output of pulumi about

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Additional context

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