Adapt CurrentUser subclass by adding cacheKey()

Change-Id: Iac1b4e40d8a347c0a317b2952a405d1fc59860d2
diff --git a/src/main/java/com/googlesource/gerrit/plugins/replication/RemoteSiteUser.java b/src/main/java/com/googlesource/gerrit/plugins/replication/RemoteSiteUser.java
index 91fce7f..31d10b6 100644
--- a/src/main/java/com/googlesource/gerrit/plugins/replication/RemoteSiteUser.java
+++ b/src/main/java/com/googlesource/gerrit/plugins/replication/RemoteSiteUser.java
@@ -35,4 +35,10 @@
   public GroupMembership getEffectiveGroups() {
     return effectiveGroups;
   }
+
+  @Override
+  public Object getCacheKey() {
+    // Never cache a remote user
+    return new Object();
+  }
 }