[ONOS-4910, ONOS-4921] Framework: utils validation and defect fix

Change-Id: I821920fa8c88e64406b702c2b8736bdeaf231474
diff --git a/plugin/src/test/resources/default/DefaultValueInLeafSubStatement.yang b/plugin/src/test/resources/default/DefaultValueInLeafSubStatement.yang
new file mode 100644
index 0000000..a78131d
--- /dev/null
+++ b/plugin/src/test/resources/default/DefaultValueInLeafSubStatement.yang
@@ -0,0 +1,15 @@
+module Test {
+    yang-version 1;
+    namespace http://huawei.com;
+    prefix Ant;
+    leaf invalid-interval {
+        type "uint16";
+        units "seconds";
+        default "1";
+        description "Interval before a route is declared invalid";
+        config true;
+        mandatory true;
+        status current;
+        reference "RFC 6020";
+    }
+}