[ONOS-4753] Identity/identityref implementation and UT

Change-Id: I40148fa228465555be3bdf410cc294ffc0f34c18
diff --git a/plugin/src/test/resources/IdentityTypedefUnresolved.yang b/plugin/src/test/resources/IdentityTypedefUnresolved.yang
new file mode 100644
index 0000000..d837fd1
--- /dev/null
+++ b/plugin/src/test/resources/IdentityTypedefUnresolved.yang
@@ -0,0 +1,16 @@
+module Test {
+    yang-version 1;
+    namespace http://huawei.com;
+    prefix Ant;
+
+    identity tunnel {
+        description
+           "Base identity from which specific tunnel types are derived.";
+    }
+
+    typedef type15 {
+        type identityref {
+             base tunnel;
+         }
+    }
+}