Adding knife wsman test to validate WSMAN/WinRM availability

This adds a command "knife wsman test" to help verify connectivity to remote WinRM endpoints.  Currently this can be tested from Windows nodes with PowerShell, but it is more difficult to validate connectivity cross platform.  This command will validate that the remote port is reachable and listening for management requests similar to Test-Wsman in PowerShell. 

Targets can be specified manually (as per the knife winrm command) or use search to identify target nodes.
I think a lot of this method already exists in https://github.com/opscode/knife-windows/blob/master/lib/chef/knife/winrm.rb -- is there a way you could re-use that code, or refactor so that both methods can use the same implementation? That way can improve and fix things in just one place.