Generate onos_app rule

There are three genrules:
 1. Build features.xml
 2. Build app.xml
 3. Generate app.oar

Change-Id: I6adfd47fadf40ad2440998071a01894458629ac6
diff --git a/buck-tools/BUCK b/buck-tools/BUCK
index 96c787a..1b8e549 100644
--- a/buck-tools/BUCK
+++ b/buck-tools/BUCK
@@ -6,6 +6,21 @@
 )
 
 python_binary(
+  name = 'onos-app-writer',
+  main = 'onos_app.py',
+  deps = [],
+  visibility = ['PUBLIC'],
+)
+
+python_binary(
+  name = 'onos-app-oar',
+  main = 'onos_oar.py',
+  deps = [],
+  visibility = ['PUBLIC'],
+)
+
+
+python_binary(
   name = 'pack_war',
   main = 'pack_war.py',
   deps = [':util'],