Add logging of cancelled replication events

Change-Id: I9a9b955b062b108f4e63bf45024a340a5c3246a8
diff --git a/src/main/java/com/googlesource/gerrit/plugins/replication/Destination.java b/src/main/java/com/googlesource/gerrit/plugins/replication/Destination.java
index eea1038..dfeb174 100644
--- a/src/main/java/com/googlesource/gerrit/plugins/replication/Destination.java
+++ b/src/main/java/com/googlesource/gerrit/plugins/replication/Destination.java
@@ -190,6 +190,9 @@
   int shutdown() {
     int cnt = 0;
     if (pool != null) {
+      for (Runnable r : pool.getQueue()) {
+        repLog.warn(String.format("Cancelling replication event %s", r));
+      }
       cnt = pool.shutdownNow().size();
       pool.unregisterWorkQueue();
       pool = null;