Revert change for windows cert pool access in 1.8

The upstream change to allow access to the windows system
cert pool was reverted, reverting and updating messaging.
Maybe 1.9....golang/go#18609

Signed-off-by: Derek McGowan <derek@mcgstyle.net> (github: dmcgowan)

Author: dmcgowan

tlsconfig/certpool_go17.go

@@ -1,4 +1,4 @@
-// +build go1.7,!go1.8
+// +build go1.7
 
 package tlsconfig
 

tlsconfig/certpool_go18.go

@@ -118,7 +118,7 @@ func Server(options Options) (*tls.Config, error) {
 		return nil, fmt.Errorf("Error reading X509 key pair (cert: %q, key: %q): %v. Make sure the key is not encrypted.", options.CertFile, options.KeyFile, err)
 	}
 	tlsConfig.Certificates = []tls.Certificate{tlsCert}
-	if options.ClientAuth >= tls.VerifyClientCertIfGiven {
+	if options.ClientAuth >= tls.VerifyClientCertIfGiven && options.CAFile != "" {
 		CAs, err := certPool(options.CAFile)
 		if err != nil {
 			return nil, err