Minor improvements to activate_instance.ps1 (#200)
Minor improvements to activate_instance.ps1 (#200)

* Use $env:ProgramFiles instead C:\Program Files

* Add Windows Server 2012 R2 Essentials license key

* Use $env:windir instead C:\Windows

Co-authored-by: Sam Eiderman <78d47a2c092b03d30654c803bdb3f14cc3673ebe@google.com>
GoogleCloudPlatform/compute-image-windows,adjackura/compute-image-windows,adjackura/compute-image-windows,GoogleCloudPlatform/compute-image-windows