support `az disk grant-access ...`

[jimdigriz]

It would be helpful to be able to use a Compute Gallery Image without having to create a blob to provide a suitable sourceVhdUri.

I understand that whilst in preview, not everything is fleshed out, but there are other SAS URIs that Azure provides, in particular the one generated by az disk grant-access ..., the output is a SAS URL to a PageBlob.

An example of creating one is:

SUB=00000000-0000-0000-0000-000000000000
RG=misc
LOC=southcentralus
NAME=aitl
az disk create \
    --subscription $SUB \
    --resource-group $RG \
    --location $LOC \
    --name $NAME \
    --gallery-image-reference /subscriptions/.../resourceGroups/.../providers/Microsoft.Compute/galleries/.../images/.../versions/... \
    --sku Premium_LRS \
    --accelerated-network true \
    --output none
az disk grant-access \
    --subscription $SUB \
    --resource-group $RG \
    --name $NAME \
    --access Read \
    --duration-in-seconds 86400 \
    --query accessSAS \
    --output tsv

Unfortunately this does not work (correlation ID f5ec4120-05d8-4056-9963-d927eedc7976) and dies with:

{"status":"Failed","error":{"code":"DeploymentFailed","target":"/subscriptions/.../providers/Microsoft.Resources/deployments/computevalidation-onboarding","message":"At least one resource deployment operation failed. Please list deployment operations for details. Please see https://aka.ms/arm-deployment-operations for usage details.","details":[{"code":"ResourceDeploymentFailure","target":"/subscriptions/.../resourceGroups/OnboardComputeValidation/providers/Microsoft.Resources/deployments/deployCloudValidationAndPlan","message":"The resource write operation failed to complete successfully, because it reached terminal provisioning state 'Failed'.","details":[{"code":"DeploymentFailed","message":"At least one resource deployment operation failed. Please list deployment operations for details. Please see https://aka.ms/arm-deployment-operations for usage details.","details":[{"code":"Conflict","message":"{\r\n  \"status\": \"Failed\",\r\n  \"error\": {\r\n    \"code\": \"ResourceDeploymentFailure\",\r\n    \"message\": \"The resource write operation failed to complete successfully, because it reached terminal provisioning state 'Failed'.\",\r\n    \"details\": [\r\n      {\r\n        \"code\": \"BadRequest\",\r\n        \"message\": \"AzCertify validation failed with status 400: {\\r\\n  \\\"error\\\": {\\r\\n    \\\"innererror\\\": {\\r\\n      \\\"internalErrorCode\\\": \\\"ParameterValueInvalid\\\"\\r\\n    },\\r\\n    \\\"code\\\": \\\"InvalidParameter\\\",\\r\\n    \\\"message\\\": \\\"The value of parameter osDiskImage.sourceVhdUri is invalid.\\\",\\r\\n    \\\"target\\\": \\\"osDiskImage.sourceVhdUri\\\"\\r\\n  }\\r\\n}\"\r\n      }\r\n    ]\r\n  }\r\n}"}]}]}]}}

Can this constraint be loosened up?