net: skip more flaky net tests on flaky net builders

e.g. https://storage.googleapis.com/go-build-log/9b937dd8/linux-arm_df54a25a.log

Change-Id: Ic5864c7bd840b4f0c6341f919fcbcd5c708b14e7
Reviewed-on: https://go-review.googlesource.com/22881Reviewed-by: Ian Lance Taylor <iant@golang.org>
Run-TryBot: Ian Lance Taylor <iant@golang.org>

src/net/lookup_test.go

@@ -70,6 +70,7 @@ func TestLookupGoogleSRV(t *testing.T) {
 	for _, tt := range lookupGoogleSRVTests {
 		cname, srvs, err := LookupSRV(tt.service, tt.proto, tt.name)
 		if err != nil {
+			testenv.SkipFlakyNet(t)
 			t.Fatal(err)
 		}
 		if len(srvs) == 0 {
@@ -137,6 +138,7 @@ func TestLookupGmailNS(t *testing.T) {
 	for _, tt := range lookupGmailNSTests {
 		nss, err := LookupNS(tt.name)
 		if err != nil {
+			testenv.SkipFlakyNet(t)
 			t.Fatal(err)
 		}
 		if len(nss) == 0 {