YANG sub module linking + unsupported yang construct + defect fix

Change-Id: I224c8c14ee2111f6844278cb540c48651544f59b
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 278c332..24744fa 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
@@ -257,6 +257,16 @@
     public static final String LISTENER_PKG = "org.onosproject.event";
 
     /**
+     * Static attribute for colon.
+     */
+    public static final String COLON = ":";
+
+    /**
+     * Static attribute for caret.
+     */
+    public static final String CARET = "^";
+
+    /**
      * Static attribute for input string.
      */
     public static final String INPUT = "input";
@@ -932,6 +942,22 @@
     public static final String YANG_UTILS_TODO = "//TODO: YANG utils generated code";
 
     /**
+     * Static attribute for YANG file error.
+     */
+    public static final String YANG_FILE_ERROR = "YANG file error : ";
+
+    /**
+     * Static attribute for unsupported error information.
+     */
+    public static final String UNSUPPORTED_YANG_CONSTRUCT = " is not supported.";
+
+    /**
+     * Static attribute for currently unsupported error information.
+     */
+    public static final String CURRENTLY_UNSUPPORTED = " is not supported in current version, please check wiki" +
+            " for YANG utils road map.";
+
+    /**
      * Creates an instance of util constants.
      */
     private UtilConstants() {