Added providerService for mastership

Change-Id: I1572161f70c696961a663cba17f197e23f96967e
diff --git a/core/api/src/main/java/org/onlab/onos/cluster/MastershipProvider.java b/core/api/src/main/java/org/onlab/onos/cluster/MastershipProvider.java
index 2cbad7f..01d91d6 100644
--- a/core/api/src/main/java/org/onlab/onos/cluster/MastershipProvider.java
+++ b/core/api/src/main/java/org/onlab/onos/cluster/MastershipProvider.java
@@ -1,7 +1,13 @@
 package org.onlab.onos.cluster;
 
+import org.onlab.onos.net.MastershipRole;
 import org.onlab.onos.net.provider.Provider;
 
+/**
+ * Abstraction of a mastership information provider.
+ */
 public interface MastershipProvider extends Provider {
-
+    // do we get role info from the local OFcontroller impl?
+    // needs to also read from distributed store and emit events?
+    // roleChanged(DeviceId deviceId, MastershipRole newRole);
 }