Add utils.Fatal, a print-to-stderr-and-exit helper

internal/utils/utils.go

@@ -273,6 +273,12 @@ func AppendIfMissing(slice []common.Address, addr common.Address) []common.Addre
 	return append(slice, addr)
 }
 
+// Fatal prints the given message onto stderr, then exits with status 1.
+func Fatal(format string, args ...interface{}) {
+	_, _ = fmt.Fprintf(os.Stderr, format, args...)
+	os.Exit(1)
+}
+
 // PrintError prints the given error in the extended format (%+v) onto stderr.
 func PrintError(err error) {
 	_, _ = fmt.Fprintf(os.Stderr, "%+v\n", err)