(maint) Only read Azure info in Azure
(maint) Only read Azure info in Azure

 - Unfortunately `Invoke-RestMethod` throws a terminating error that
   can't be ignored with `-ErrorAction SilentlyContinue`. So instead
   detect an Azure environment first before querying the Azure metadata
   endpoint.

 - This allows diagnostic info to be acquired when running an Azure
   agent in a non-Azure VM.

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