[COOK-4130] Support Powershell 3.0 and 4.0

Signed-off-by: Sean OMeara <someara@opscode.com>
[COOK-4132] Warn people to use Chef's built-in powershell_script resource if on Chef >= 11.6.0

Signed-off-by: Sean OMeara <someara@opscode.com>