build: update logging statements to make json log work - fixes #6038

This changes log statements from log to fs package, which is required for --use-json-log
to properly make log output in JSON format. The recently added custom linting rule,
handled by ruleguard via gocritic via golangci-lint, warns about these and suggests
the alternative. Fixing was therefore basically running "golangci-lint run --fix",
although some manual fixup of mainly imports are necessary following that.

fs/log/syslog_unix.go

@@ -42,12 +42,12 @@ var (
 func startSysLog() bool {
 	facility, ok := syslogFacilityMap[Opt.SyslogFacility]
 	if !ok {
-		log.Fatalf("Unknown syslog facility %q - man syslog for list", Opt.SyslogFacility)
+		fs.Fatalf(nil, "Unknown syslog facility %q - man syslog for list", Opt.SyslogFacility)
 	}
 	Me := path.Base(os.Args[0])
 	w, err := syslog.New(syslog.LOG_NOTICE|facility, Me)
 	if err != nil {
-		log.Fatalf("Failed to start syslog: %v", err)
+		fs.Fatalf(nil, "Failed to start syslog: %v", err)
 	}
 	log.SetFlags(0)
 	log.SetOutput(w)