Fix help text being incorrect with multiple args

E.g. "docker foobar run" would have printed "Command not found:
foobar" and printed the help text for "run". It should instead
print the root help message for docker.

Signed-off-by: Ben Firshman <ben@firshman.co.uk>

api/client/cli.go

@@ -75,11 +75,11 @@ func (cli *DockerCli) Cmd(args ...string) error {
 		method, exists := cli.getMethod(args[0])
 		if !exists {
 			fmt.Println("Error: Command not found:", args[0])
-			return cli.CmdHelp(args[1:]...)
+			return cli.CmdHelp()
 		}
 		return method(args[1:]...)
 	}
-	return cli.CmdHelp(args...)
+	return cli.CmdHelp()
 }
 
 func (cli *DockerCli) Subcmd(name, signature, description string) *flag.FlagSet {