all: disable log message colors outside of geth

Also tweak behaviour so colors are only enabled when stderr is a terminal.

cmd/bootnode/main.go

@@ -50,7 +50,7 @@ func main() {
 	)
 	flag.Parse()
 
-	glogger := log.NewGlogHandler(log.StreamHandler(os.Stderr, log.TerminalFormat()))
+	glogger := log.NewGlogHandler(log.StreamHandler(os.Stderr, log.TerminalFormat(false)))
 	glogger.Verbosity(log.Lvl(*verbosity))
 	glogger.Vmodule(*vmodule)
 	log.Root().SetHandler(glogger)