Added method getRegisteredApplications

Change-Id: Ic741dfcca84fd72fd2ab236bef97cfeadc890d16
diff --git a/core/api/src/main/java/org/onosproject/app/ApplicationService.java b/core/api/src/main/java/org/onosproject/app/ApplicationService.java
index 51d3eb4..0f2d155 100644
--- a/core/api/src/main/java/org/onosproject/app/ApplicationService.java
+++ b/core/api/src/main/java/org/onosproject/app/ApplicationService.java
@@ -15,6 +15,7 @@
  */
 package org.onosproject.app;
 
+import com.google.common.collect.ImmutableSet;
 import org.onosproject.core.Application;
 import org.onosproject.core.ApplicationId;
 import org.onosproject.event.ListenerService;
@@ -85,4 +86,14 @@
     default InputStream getApplicationArchive(ApplicationId appId) {
         return null;
     }
+
+    /**
+     * Returns the set of all installed applications.
+     *
+     * @return set of apps putside the build/core environment
+     */
+    default Set<Application> getRegisteredApplications() {
+        return ImmutableSet.of();
+    }
+
 }