Adding application level dependencies between dependent models.

Change-Id: I3b37da04c962094852d47d24e49287ce30648016
diff --git a/bucklets/yang.bucklet b/bucklets/yang.bucklet
index d9a2df0..7769fe4 100644
--- a/bucklets/yang.bucklet
+++ b/bucklets/yang.bucklet
@@ -22,6 +22,7 @@
     url = 'http://onosproject.org',
     description = None,
     deps = [],
+    required_apps = [],
     **kwargs
     ):
 
@@ -73,7 +74,7 @@
       category = 'Models',
       url = url,
       description = description,
-      required_apps = [ 'org.onosproject.yang' ],
+      required_apps = required_apps + [ 'org.onosproject.yang' ],
     )
 
 def yang_osgi_jar(