mark some obvious tests as :windows_only

Recent changes made `spec/unit/provider/service/windows.rb` fail on some non-windows platforms, due to stubbing. Rather than try to make the stubs work for non-windows, just mark the test as `:windows_only`. Also marked some obvious windows-only specs.
I think there's a bonus "end" here due to skipping one level of indentation which is causing travis failures.