HADOOP-12485 Don't prefer IPV4 stack on tests.

hadoop-project/pom.xml

@@ -1140,7 +1140,10 @@
             <test.cache.data>${test.cache.data}</test.cache.data>
             <test.build.classes>${test.build.classes}</test.build.classes>
 
-            <java.net.preferIPv4Stack>true</java.net.preferIPv4Stack>
+            <!-- Prefer ipv6 if it's there use -Ptest-ipv4 to turn off. -->
+            <java.net.preferIPv4Stack>false</java.net.preferIPv4Stack>
+            <java.net.preferIPv6Addresses>true</java.net.preferIPv6Addresses>
+
             <java.security.krb5.conf>${project.build.directory}/test-classes/krb5.conf</java.security.krb5.conf>
             <java.security.egd>${java.security.egd}</java.security.egd>
             <require.test.libhadoop>${require.test.libhadoop}</require.test.libhadoop>
@@ -1316,5 +1319,25 @@
         </plugins>
       </build>
     </profile>
+    <profile>
+        <id>test-ipv4</id>
+        <activation>
+            <activeByDefault>false</activeByDefault>
+        </activation>
+        <build>
+            <plugins>
+                <plugin>
+                    <groupId>org.apache.maven.plugins</groupId>
+                    <artifactId>maven-surefire-plugin</artifactId>
+                    <configuration>
+                        <systemPropertyVariables>
+                            <java.net.preferIPv4Stack>false</java.net.preferIPv4Stack>
+                            <java.net.preferIPv6Addresses>false</java.net.preferIPv6Addresses>
+                        </systemPropertyVariables>
+                    </configuration>
+                </plugin>
+            </plugins>
+        </build>
+    </profile>
   </profiles>
 </project>