use AddError everywhere (#2372)

plugins/inputs/iptables/iptables.go

@@ -54,20 +54,19 @@ func (ipt *Iptables) Gather(acc telegraf.Accumulator) error {
 	}
 	// best effort : we continue through the chains even if an error is encountered,
 	// but we keep track of the last error.
-	var err error
 	for _, chain := range ipt.Chains {
 		data, e := ipt.lister(ipt.Table, chain)
 		if e != nil {
-			err = e
+			acc.AddError(e)
 			continue
 		}
 		e = ipt.parseAndGather(data, acc)
 		if e != nil {
-			err = e
+			acc.AddError(e)
 			continue
 		}
 	}
-	return err
+	return nil
 }
 
 func (ipt *Iptables) chainList(table, chain string) (string, error) {

plugins/inputs/iptables/iptables_test.go

@@ -141,7 +141,7 @@ func TestIptables_Gather(t *testing.T) {
 			},
 		}
 		acc := new(testutil.Accumulator)
-		err := ipt.Gather(acc)
+		err := acc.GatherError(ipt.Gather)
 		if !reflect.DeepEqual(tt.err, err) {
 			t.Errorf("%d: expected error '%#v' got '%#v'", i, tt.err, err)
 		}
@@ -199,7 +199,7 @@ func TestIptables_Gather_listerError(t *testing.T) {
 		},
 	}
 	acc := new(testutil.Accumulator)
-	err := ipt.Gather(acc)
+	err := acc.GatherError(ipt.Gather)
 	if !reflect.DeepEqual(err, errFoo) {
 		t.Errorf("Expected error %#v got\n%#v\n", errFoo, err)
 	}