chef-shell checks platform when looking for client.rb and solo.rb.
https://github.com/opscode/chef/issues/2380 pointed out that on
windows, -c is required with the -z flag because it would assume
nix and look in /etc/chef for client.rb
Merge pull request #2395 from opscode/jdmundrawala/chef-shell-windows

chef-shell checks platform when looking for client.rb and solo.rb.