all: disable log message colors outside of geth

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

cmd/wnode/main.go

@@ -152,7 +152,7 @@ func echo() {
 }
 
 func initialize() {
-	log.Root().SetHandler(log.LvlFilterHandler(log.Lvl(*argVerbosity), log.StreamHandler(os.Stderr, log.TerminalFormat())))
+	log.Root().SetHandler(log.LvlFilterHandler(log.Lvl(*argVerbosity), log.StreamHandler(os.Stderr, log.TerminalFormat(false))))
 
 	done = make(chan struct{})
 	var peers []*discover.Node