Added graceful shutdown for upstart service.
Reworked slightly the mastership & device managers and stores to make it work (sort-of) in the distributed env.
diff --git a/core/trivial/src/main/java/org/onlab/onos/net/trivial/impl/SimpleClusterStore.java b/core/trivial/src/main/java/org/onlab/onos/net/trivial/impl/SimpleClusterStore.java
index 782b389..c782530 100644
--- a/core/trivial/src/main/java/org/onlab/onos/net/trivial/impl/SimpleClusterStore.java
+++ b/core/trivial/src/main/java/org/onlab/onos/net/trivial/impl/SimpleClusterStore.java
@@ -62,4 +62,8 @@
         return ControllerNode.State.ACTIVE;
     }
 
+    @Override
+    public void removeNode(NodeId nodeId) {
+    }
+
 }