Fixes for Compute Admin

[MatthewMcGlynn]

1. Reverting to Add-AzureRMVHD –
   a. I found the reason that Set-AzureRMBlobContent was faster. It turns out that the latter method leaves the VHD as dynamic when it makes its way into the PIR. This can cause a number of issues later on with VM lifecycle operations since CRP does not support dynamic disks. Add-AzureRMVHD implicitly makes it fixed by turning into a Page Blob.
2. Stopping on credential validation errors immediately
   a. This helps us prevent users from getting too far before we catch simple issues like ARM Endpoint parameters and creds mistakes
3. Token refreshing on the download portion so that we don’t get issues with the token timing out
   a. Tokens refresh every 5 minutes on the download
4. Fixed minor issues with Remove-VMImage
5. Idempotency Fixes (major chunks for now)
   a. Check for the existence of the VHD – this suggests that the last state was a download or upload error (skip VHD creation)
   b. Check for the existence of the VM Image – this suggests the VM Image made its way into the PIR, but that the Marketplace item component failed (skip VHD creation and upload/download)
6. Added validation to check that the ARM endpoint specified is valid – catches typos or bad endpoint for environment
7. Added retry logic for downloading Marketplace item pre-reqs in case of connection dropping
8. Added a stronger check for idempotent logic to get around the time it took for the previous check to work as expected

[msftclas]

@MatthewMcGlynn,
Thanks for your contribution as a Microsoft full-time employee or intern. You do not need to sign a CLA.
Thanks,
Microsoft Pull Request Bot

[MatthewMcGlynn]

Also included is handling Azure Stack module 1.2.8 and 1.2.9 for Compute Admin

[MatthewMcGlynn]

Validation Confirmed - Merging.