[ONOS-6869] Move blocking DocumentTree to core primitives package and implement default methods for constructing blocking primitives

Change-Id: I9c227a690a120dba7d9d89c6c9178c8b357b52aa
diff --git a/core/api/src/main/java/org/onosproject/store/service/DocumentTree.java b/core/api/src/main/java/org/onosproject/store/service/DocumentTree.java
index e8e4746..ad6d405 100644
--- a/core/api/src/main/java/org/onosproject/store/service/DocumentTree.java
+++ b/core/api/src/main/java/org/onosproject/store/service/DocumentTree.java
@@ -26,7 +26,12 @@
  * @param <V> document tree value type
  */
 @NotThreadSafe
-public interface DocumentTree<V> {
+public interface DocumentTree<V> extends DistributedPrimitive {
+
+    @Override
+    default Type primitiveType() {
+        return Type.DOCUMENT_TREE;
+    }
 
     /**
      * Returns the {@link DocumentPath path} to root of the tree.