Log custom plugin stderr only if the status is not ok.

Otherwise with plugins that run frequently and report ok status, the
logs are filled with unnecessary noise and significantly increases log
size.

pkg/custompluginmonitor/plugin/plugin.go

@@ -89,7 +89,7 @@ func (p *Plugin) Run() {
 
 // run each rule in parallel and wait for them to complete
 func (p *Plugin) runRules() {
-	glog.Info("Start to run custom plugins")
+	glog.V(3).Info("Start to run custom plugins")
 
 	for _, rule := range p.config.Rules {
 		p.syncChan <- struct{}{}
@@ -120,7 +120,7 @@ func (p *Plugin) runRules() {
 	}
 
 	p.Wait()
-	glog.Info("Finish running custom plugins")
+	glog.V(3).Info("Finish running custom plugins")
 }
 
 // readFromReader reads the maxBytes from the reader and drains the rest.
@@ -203,12 +203,6 @@ func (p *Plugin) run(rule cpmtypes.CustomRule) (exitStatus cpmtypes.Status, outp
 		}
 	}
 
-	// log the stderr from the plugin
-	if len(stderr) != 0 {
-		glog.Infof("Start logs from plugin %q \n %s", rule.Path, string(stderr))
-		glog.Infof("End logs from plugin %q", rule.Path)
-	}
-
 	// trim suffix useless bytes
 	output = string(stdout)
 	output = strings.TrimSpace(output)
@@ -227,8 +221,10 @@ func (p *Plugin) run(rule cpmtypes.CustomRule) (exitStatus cpmtypes.Status, outp
 	case 0:
 		return cpmtypes.OK, output
 	case 1:
+		logPluginStderr(rule.Path, string(stderr))
 		return cpmtypes.NonOK, output
 	default:
+		logPluginStderr(rule.Path, string(stderr))
 		return cpmtypes.Unknown, output
 	}
 }
@@ -237,3 +233,10 @@ func (p *Plugin) Stop() {
 	p.tomb.Stop()
 	glog.Info("Stop plugin execution")
 }
+
+func logPluginStderr(path, logs string) {
+	if len(logs) != 0 {
+		glog.Infof("Start logs from plugin %q \n %s", path, string(logs))
+		glog.Infof("End logs from plugin %q", path)
+	}
+}