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/api/src/main/java/org/onlab/onos/cluster/ClusterAdminService.java b/core/api/src/main/java/org/onlab/onos/cluster/ClusterAdminService.java
new file mode 100644
index 0000000..4f98804
--- /dev/null
+++ b/core/api/src/main/java/org/onlab/onos/cluster/ClusterAdminService.java
@@ -0,0 +1,15 @@
+package org.onlab.onos.cluster;
+
+/**
+ * Service for administering the cluster node membership.
+ */
+public interface ClusterAdminService {
+
+ /**
+ * Removes the specified node from the cluster node list.
+ *
+ * @param nodeId controller node identifier
+ */
+ void removeNode(NodeId nodeId);
+
+}