Fix issue with indexing tasks queue

IndexEventHandler contains a mechanism to prevent multiple indexing task
from being queued for the same id. That mechanism is based on a shared
queue instance. Before this change IndexEventHandler wasn't a singleton
so for each event a new instance was created and each event had its own
instance of the queue.

Bug: Issue 9941
Change-Id: Id9a8f288816fa56389aae65e3c29aa7ca40410cb

src/main/java/com/ericsson/gerrit/plugins/highavailability/index/IndexModule.java

diff --git a/src/main/java/com/ericsson/gerrit/plugins/highavailability/index/IndexModule.java b/src/main/java/com/ericsson/gerrit/plugins/highavailability/index/IndexModule.java
index 9d0d03d..4a25fc8 100644
--- a/src/main/java/com/ericsson/gerrit/plugins/highavailability/index/IndexModule.java
+++ b/src/main/java/com/ericsson/gerrit/plugins/highavailability/index/IndexModule.java
@@ -36,7 +36,9 @@
         .toProvider(ForwardedIndexExecutorProvider.class);
     bind(IndexEventLocks.class).in(Scopes.SINGLETON);
     listener().to(IndexExecutorProvider.class);
-    DynamicSet.bind(binder(), ChangeIndexedListener.class).to(IndexEventHandler.class);
+    DynamicSet.bind(binder(), ChangeIndexedListener.class)
+        .to(IndexEventHandler.class)
+        .in(Scopes.SINGLETON);
     DynamicSet.bind(binder(), AccountIndexedListener.class).to(IndexEventHandler.class);
     DynamicSet.bind(binder(), GroupIndexedListener.class).to(IndexEventHandler.class);
     DynamicSet.bind(binder(), ProjectIndexedListener.class).to(IndexEventHandler.class);