Due to design of mixlib options, we need to include the additional flags similar to knife-windows (https://github.com/opscode/knife-windows/blob/master/lib/chef/knife/winrm_base.rb)
Since the knife bootstrap code does not provide a module we end up having these duplicated here. 

If the bootstrap (https://github.com/opscode/chef/blob/master/lib/chef/knife/bootstrap.rb) had exposed it as a module, we wont have duplicate copies like these and would be easy to maintain during future changes.

A cleaner approach would be to refactor the bootstrap code within chef/knife and knife-windows, which i believe is in pipeline for knife-windows refactoring later?