Removed usage of the headless key from the parallels-iso builder in the win2012r2-standard.json template as it seems to not be part of packer 1.5.1's schema.
Removed usage of the headless key from the parallels-iso builder in the win2012r2-standard.json template as it seems to not be part of packer 1.5.1's schema.

boxcutter/windows,HirotakaKato/boxcutter-windows-ja,HirotakaKato/boxcutter-windows-ja,boxcutter/windows,boxcutter/windows,HirotakaKato/boxcutter-windows-ja