Update git submodules

* Update plugins/replication from branch 'stable-2.16'
  to 18857e12579d841693c2dc39e9ee330ab36bca65
  - Fix NPE when username or password isn't specified for remote
    
    When the username or password is not specified, pass an empty
    string instead of null.
    
    Change-Id: I49121b9873eb9f2800417b6d264cc2ad82047f85
    
diff --git a/plugins/replication b/plugins/replication
index ed5c9f2..18857e1 160000
--- a/plugins/replication
+++ b/plugins/replication
@@ -1 +1 @@
-Subproject commit ed5c9f26b255fe915ba9abfad77771728fc0d3d8
+Subproject commit 18857e12579d841693c2dc39e9ee330ab36bca65