Event history service and CLI

- Tool created while debugging ONOS-3509

  Usage Example: (See recent Mastership and Device events)
   onos> events -m -d

Change-Id: I87aceaf8fe61732a61c2d1e39399d0f10a729b54
diff --git a/apps/events/src/main/java/org/onosproject/events/EventHistoryService.java b/apps/events/src/main/java/org/onosproject/events/EventHistoryService.java
new file mode 100644
index 0000000..f653c53
--- /dev/null
+++ b/apps/events/src/main/java/org/onosproject/events/EventHistoryService.java
@@ -0,0 +1,41 @@
+/*
+ * Copyright 2016 Open Networking Laboratory
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package org.onosproject.events;
+
+import java.util.Deque;
+
+import org.onosproject.event.Event;
+
+import com.google.common.annotations.Beta;
+
+/**
+ * Provides history of instance local ONOS Events.
+ */
+@Beta
+public interface EventHistoryService {
+
+    /**
+     * Returns unmodifiable view of ONOS events history.
+     *
+     * @return ONOS events (First element is the oldest event stored)
+     */
+    Deque<Event<?, ?>> history();
+
+    /**
+     * Clears all stored history.
+     */
+    void clear();
+}