Correct unit test flaw introduced in 54c9ecf682

Motivation:
54c9ecf682 introduced a unit tests which attempted to exclude addresses which resolved to loop back addresses from an assert statement. This was done with a static check for localhost but depending on machine configuration it is possible for other interfaces to be resolved.

Modifications:
- Use InetAddress#isLoopbackAddress() instead of string match on localhost

Result:
DnsNameResolverTest#testNameServerCache is more reliable.

resolver-dns/src/test/java/io/netty/resolver/dns/DnsNameResolverTest.java

@@ -385,7 +385,7 @@ public class DnsNameResolverTest {
             try {
                 final Map<String, InetAddress> resultA = testResolve0(resolver, EXCLUSIONS_RESOLVE_A);
                 for (Entry<String, InetAddress> resolvedEntry : resultA.entrySet()) {
-                    if (resolvedEntry.getValue().getHostAddress().equalsIgnoreCase("localhost")) {
+                    if (resolvedEntry.getValue().isLoopbackAddress()) {
                         continue;
                     }
                     if (overridenHostnames.contains(resolvedEntry.getKey())) {