go report card fixes (#3182)

Went over the list at https://goreportcard.com/report/github.com/coredns/coredns
and removed/fix some code to make it slightly happier.

Signed-off-by: Miek Gieben <miek@miek.nl>

test/secondary_test.go

@@ -73,7 +73,7 @@ func TestSecondaryZoneTransfer(t *testing.T) {
 	var r *dns.Msg
 	// This is now async; we need to wait for it to be transferred.
 	for i := 0; i < 10; i++ {
-		r, err = dns.Exchange(m, udp)
+		r, _ = dns.Exchange(m, udp)
 		if len(r.Answer) != 0 {
 			break
 		}