Hide command options that are related to Windows

Signed-off-by: Boaz Shuster <ripcurld.github@gmail.com>

ping.go

@@ -7,7 +7,7 @@ import (
 	"golang.org/x/net/context"
 )
 
-// Ping pings the server and returns the value of the "Docker-Experimental" & "API-Version" headers
+// Ping pings the server and returns the value of the "Docker-Experimental", "OS-Type" & "API-Version" headers
 func (cli *Client) Ping(ctx context.Context) (types.Ping, error) {
 	var ping types.Ping
 	req, err := cli.buildRequest("GET", fmt.Sprintf("%s/_ping", cli.basePath), nil, nil)
@@ -26,5 +26,7 @@ func (cli *Client) Ping(ctx context.Context) (types.Ping, error) {
 		ping.Experimental = true
 	}
 
+	ping.OSType = serverResp.header.Get("OSType")
+
 	return ping, nil
 }