iptables lister未初始化问题 (#995)

* iptables插件

* 添加注册

* pushgateway接口支持用户指定值置换agent_hostname

* pushgateway接口支持用户指定值置换agent_hostname

* 修改命名

* Update iptables.go

修复未初始化问题 #994

inputs/iptables/iptables.go

@@ -62,6 +62,9 @@ func (ins *Instance) Init() error {
 		log.Println("W! Table or Chains is empty")
 		return types.ErrInstancesEmpty
 	}
+	if ins.lister == nil {
+		ins.lister = ins.chainList
+	}
 	return nil
 }
 
@@ -71,6 +74,10 @@ func (ins *Instance) Gather(slist *types.SampleList) {
 		log.Println("W! Table or Chains is empty")
 		return
 	}
+	if ins.lister == nil {
+		log.Println("E! Lister is empty or not initialized")
+		return
+	}
 	// best effort : we continue through the chains even if an error is encountered,
 	// but we keep track of the last error.
 	for _, chain := range ins.Chains {