Workaround issue 150
Workaround issue 150

- The ngen step fails on some OS/.NET combinations (maybe all). Since the compilation is optional, just continue even if it fails. This likely won't be fixed without using an elevated powershell provisioner over winrm.

tsew/packer-windows,floradu88/packer-windows,joefitzgerald/packer-windows,TheBigBear/packer-windows-joefitzgerald,bigwave/packer-windows,TaylorMonacelli/packer-windows