Pretty-print stored ref-updates for replication

Allow having a more understandable printing of the stored
ref-update events when printed in the logs.

Change-Id: I8d7fd1bfb89a1ff39d89395aace7c473bb3004ed

src/main/java/com/googlesource/gerrit/plugins/replication/EventsStorage.java

diff --git a/src/main/java/com/googlesource/gerrit/plugins/replication/EventsStorage.java b/src/main/java/com/googlesource/gerrit/plugins/replication/EventsStorage.java
index d6ae6b4..0efa726 100644
--- a/src/main/java/com/googlesource/gerrit/plugins/replication/EventsStorage.java
+++ b/src/main/java/com/googlesource/gerrit/plugins/replication/EventsStorage.java
@@ -37,6 +37,11 @@
   public static class ReplicateRefUpdate {
     public String project;
     public String ref;
+
+    @Override
+    public String toString() {
+      return "ref-update " + project + ":" + ref;
+    }
   }
 
   private static Gson GSON = new Gson();