Add k8s tags to related tests (#1018)

, so that `make test` will pass by default.

Also fixed several ineffassign and golint issues.

Signed-off-by: Yong Tang <yong.tang.github@outlook.com>

test/kubernetes_api_fallthrough_test.go

@@ -0,0 +1,53 @@
+// +build k8s
+
+package test
+
+import (
+	"testing"
+	"time"
+
+	"github.com/coredns/coredns/middleware/test"
+
+	"github.com/miekg/dns"
+)
+
+func TestKubernetesAPIFallthrough(t *testing.T) {
+	tests := []test.Case{
+		{
+			Qname: "svc-1-a.test-1.svc.cluster.local.", Qtype: dns.TypeA,
+			Rcode: dns.RcodeSuccess,
+			Answer: []dns.RR{
+				test.A("svc-1-a.test-1.svc.cluster.local.      303    IN      A       10.0.0.100"),
+			},
+		},
+	}
+
+	corefile :=
+		`.:0 {
+    kubernetes cluster.local {
+        endpoint http://nonexistance:8080,http://invalidip:8080,http://localhost:8080
+        namespaces test-1
+        pods disabled
+    }`
+
+	server, udp, _, err := CoreDNSServerAndPorts(corefile)
+	if err != nil {
+		t.Fatalf("Could not get CoreDNS serving instance: %s", err)
+	}
+	defer server.Stop()
+
+	// Work-around for timing condition that results in no-data being returned in test environment.
+	time.Sleep(3 * time.Second)
+
+	for _, tc := range tests {
+
+		c := new(dns.Client)
+		m := tc.Msg()
+
+		res, _, err := c.Exchange(m, udp)
+		if err != nil {
+			t.Fatalf("Could not send query: %s", err)
+		}
+		test.SortAndCheck(t, res, tc)
+	}
+}