Run tests in parallel (#478)

Create a small speedup running the tests:

PASS
ok  	github.com/miekg/coredns/test	10.329s

PASS
ok  	github.com/miekg/coredns/test	6.079s

Skip the etcd ones. Doing the middleware/*/*_test ones doesn't yield
any speedup as these are still done on a per directory basis.

test/kubernetes_test.go

@@ -242,6 +242,7 @@ func createTestServer(t *testing.T, corefile string) (*caddy.Instance, string) {
 }
 
 func TestKubernetesIntegration(t *testing.T) {
+	t.Parallel()
 	corefile :=
 		`.:0 {
     kubernetes cluster.local 0.0.10.in-addr.arpa {