May need to change "PremiumLRS" to "Premium_LRS"

[Jongchan]

Hi, I am currently converting VM image to have Managed Disks.
thanks to your code, I am almost done with the conversion.

During the conversion, I faced "CloseError" and noticed that the string for StorageAccountType was "Standard_LRS" before conversion. Thus I suspected that the string should be set as "Premium_LRS" instead of "PremiumLRS", which is written in your code snippet.

Anyways, thanks for sharing a good snippet, and please revise if I am correct.