CS-15356: cloudstack 3.0 API - updateZone API - when internaldns2 parameter is not being passed to updateZone API, leave it as is (i.e. remain original value of internaldns2).

server/src/com/cloud/configuration/ConfigurationManagerImpl.java

@@ -1427,6 +1427,10 @@ public class ConfigurationManagerImpl implements ConfigurationManager, Configura
             internalDns1 = zone.getInternalDns1();
         }
 
+        if (internalDns2 == null) {
+        	internalDns2 = zone.getInternalDns2();
+        }
+        
         if (guestCidr == null) {
             guestCidr = zone.getGuestNetworkCidr();
         }