cmd/cli: adopt FilteredLevelWriter when doing internal logging

Without verbose log, we use internal log writer with log level set to
debug. However, this will affect other writers, like console log, since
they are default to notice level.

By adopting FilteredLevelWriter, we can make internal log writer run in
debug level, but all others will run in default level instead.

cmd/cli/prog.go

@@ -514,13 +514,13 @@ func (p *prog) run(reload bool, reloadCh chan struct{}) {
 	if !reload {
 		// Stop writing log to unix socket.
 		consoleWriter.Out = os.Stdout
-		initLoggingWithBackup(false)
+		logWriters := initLoggingWithBackup(false)
 		if p.logConn != nil {
 			_ = p.logConn.Close()
 		}
 		go p.apiConfigReload()
 		p.postRun()
-		p.initInternalLogging()
+		p.initInternalLogging(logWriters)
 	}
 	wg.Wait()
 }