Added a WallClockTimestamp and associated interface/implementation for generating it. This will be used by the initial implementation of distributed host store
diff --git a/core/store/dist/src/main/java/org/onlab/onos/store/host/impl/HostClockManager.java b/core/store/dist/src/main/java/org/onlab/onos/store/host/impl/HostClockManager.java
new file mode 100644
index 0000000..49eeb06
--- /dev/null
+++ b/core/store/dist/src/main/java/org/onlab/onos/store/host/impl/HostClockManager.java
@@ -0,0 +1,38 @@
+package org.onlab.onos.store.host.impl;
+
+import static org.slf4j.LoggerFactory.getLogger;
+
+import org.apache.felix.scr.annotations.Activate;
+import org.apache.felix.scr.annotations.Component;
+import org.apache.felix.scr.annotations.Deactivate;
+import org.apache.felix.scr.annotations.Service;
+import org.onlab.onos.net.host.HostClockService;
+import org.onlab.onos.store.Timestamp;
+import org.onlab.onos.store.impl.WallClockTimestamp;
+import org.onlab.packet.MacAddress;
+import org.slf4j.Logger;
+
+/**
+ * HostClockService to issue Timestamps based on local wallclock time.
+ */
+@Component(immediate = true)
+@Service
+public class HostClockManager implements HostClockService {
+
+    private final Logger log = getLogger(getClass());
+
+    @Activate
+    public void activate() {
+        log.info("Started");
+    }
+
+    @Deactivate
+    public void deactivate() {
+        log.info("Stopped");
+    }
+
+    @Override
+    public Timestamp getTimestamp(MacAddress hostMac) {
+        return new WallClockTimestamp();
+    }
+}