Refactor: add static factory method in BatchWrite, instead of in IntentStore

Change-Id: Ic0cecc4b3cc4facbc469d2eb87a36c4d5166a6f2
diff --git a/core/api/src/main/java/org/onosproject/net/intent/BatchWrite.java b/core/api/src/main/java/org/onosproject/net/intent/BatchWrite.java
index e030036..d528e28 100644
--- a/core/api/src/main/java/org/onosproject/net/intent/BatchWrite.java
+++ b/core/api/src/main/java/org/onosproject/net/intent/BatchWrite.java
@@ -24,7 +24,7 @@
 
 import static com.google.common.base.Preconditions.checkNotNull;
 
-public class BatchWrite {
+public final class BatchWrite {
 
     public enum OpType {
         CREATE_INTENT,
@@ -36,6 +36,17 @@
 
     List<Operation> operations = new ArrayList<>();
 
+    private BatchWrite() {}
+
+    /**
+     * Returns a new empty batch write operation builder.
+     *
+     * @return BatchWrite
+     */
+    public static BatchWrite newInstance() {
+        return new BatchWrite();
+    }
+
     public List<Operation> operations() {
         return Collections.unmodifiableList(operations);
     }