[ONOS-4636]YANG Grouping linking bug fix + YANG Code review comment fix

Change-Id: I68ee8dd08266a02593e217cef1a9bb010037d673
diff --git a/utils/yangutils/src/main/java/org/onosproject/yangutils/utils/UtilConstants.java b/utils/yangutils/src/main/java/org/onosproject/yangutils/utils/UtilConstants.java
index 7e89998..adc7015 100644
--- a/utils/yangutils/src/main/java/org/onosproject/yangutils/utils/UtilConstants.java
+++ b/utils/yangutils/src/main/java/org/onosproject/yangutils/utils/UtilConstants.java
@@ -966,6 +966,7 @@
      * Static attribute for augmentable.
      */
     public static final String AUGMENTABLE = "Augmentable";
+
     /**
      * Static attribute for list.
      */
@@ -1018,6 +1019,11 @@
     public static final String COMPONENT_ANNOTATION = "@Component";
 
     /**
+     * Static attribute for component.
+     */
+    public static final String COMPONENT = "Component";
+
+    /**
      * Static attribute for immediate.
      */
     public static final String IMMEDIATE = "immediate";
@@ -1134,6 +1140,16 @@
             + "grouping for given uses";
 
     /**
+     * Static attribute for reference.
+     */
+    public static final String REFERENCE = "Reference";
+
+    /**
+     * Static attribute for ReferenceCardinality.
+     */
+    public static final String REFERENCE_CARDINALITY = "ReferenceCardinality";
+
+    /**
      * Creates an instance of util constants.
      */
     private UtilConstants() {