test: make test-net-connect-options-ipv6.js better

improve the robustness of test-net-connect-options-ipv6.js

PPC Suse build team encountered intermittent failures related
to dns.  Improve test to make it more robust in the face
of intermittent dns issues.

test/parallel/test-net-connect-options-ipv6.js

@@ -40,7 +40,21 @@ function tryConnect() {
       server.close();
     });
   }).on('error', function(err) {
-    if (err.syscall === 'getaddrinfo' && err.code === 'ENOTFOUND') {
+    // ENOTFOUND means we don't have the requested address. In this
+    // case we try the next one in the list and if we run out of
+    // candidates we assume IPv6 is not supported on the
+    // machine and skip the test.
+    // EAI_AGAIN means we tried to remotely resolve the address and
+    // timed out or hit some intermittent connectivity issue with the
+    // dns server.  Although we are looking for local loopback addresses
+    // we may go remote since the list we search includes addresses that
+    // cover more than is available on any one distribution. The
+    // net is that if we get an EAI_AGAIN we were looking for an
+    // address which does not exist in this distribution so the error
+    // is not significant and we should just move on and try the
+    // next address in the list.
+    if ((err.syscall === 'getaddrinfo') && ((err.code === 'ENOTFOUND') ||
+                                            (err.code === 'EAI_AGAIN'))) {
       if (host !== 'localhost' || --localhostTries === 0)
         host = hosts[++hostIdx];
       if (host)