inital term info service

Change-Id: I4503f1dcadda62bb25e2dba106e9a1101b4d37d6

+package org.onlab.onos.cluster;
+
+public class MastershipTerm {
+    private final NodeId master = null;
+    private int termNumber;
+}

+package org.onlab.onos.cluster;
+
+import org.onlab.onos.net.DeviceId;
+
+// TODO give me a better name
+/**
+ * Service to obtain mastership term information.
+ */
+public interface MastershipTermService {
+
+    // TBD: manage/increment per device mastership change
+    //      or increment on any change
+    /**
+     * Returns the term number of mastership change occurred for given device.
+     *
+     * @param deviceId the identifier of the device
+     * @return current master's term.
+     */
+    MastershipTerm getMastershipTerm(DeviceId deviceId);
+}