add setting field default value

Author: hengboy

src/main/java/org/minbox/framework/mongo/client/setting/ClusterSettings.java

@@ -14,8 +14,8 @@
 @Data
 public class ClusterSettings {
     private ClusterConnectionMode mode;
-    private ClusterType requiredClusterType;
+    private ClusterType requiredClusterType = ClusterType.UNKNOWN;
     private String requiredReplicaSetName;
-    private long localThresholdMilliSeconds;
-    private long serverSelectionTimeoutMilliSeconds;
+    private long localThresholdMilliSeconds = 15;
+    private long serverSelectionTimeoutMilliSeconds = 30000;
 }