Added scalable gateway app to BUCK app list

And fixed maven artifact ID to follow the convention

Change-Id: I700c93516d4c79a3b5b93e99138a593a569e52a1
diff --git a/apps/scalablegateway/pom.xml b/apps/scalablegateway/pom.xml
index e84168d..a79429e 100644
--- a/apps/scalablegateway/pom.xml
+++ b/apps/scalablegateway/pom.xml
@@ -25,7 +25,7 @@
         <version>1.7.0-SNAPSHOT</version>
     </parent>
 
-    <artifactId>onos-scalablegateway</artifactId>
+    <artifactId>onos-app-scalablegateway</artifactId>
     <packaging>bundle</packaging>
 
     <description>ONOS Scalable Gateway applications</description>