Download aws-dynamodb-refdb when multi-site is enabled

The aws-dynamodb-refdb plugin is not only needed when running a
single-site in HA but also when deploying a multi-site.

Fix bug introduced by I5012c15a, where zookeeper was not correctly
replaced by dynamodb when multi-site was enabled.

Bug: Issue 15347
Change-Id: I80b42fe591fdf8fa4c145dc212c166d19d2bd520
diff --git a/dual-primary/Makefile b/dual-primary/Makefile
index 6c4a479..1535493 100644
--- a/dual-primary/Makefile
+++ b/dual-primary/Makefile
@@ -17,7 +17,7 @@
 HA_SITE_PLUGINS=$(SINGLE_SITE_PLUGINS) aws-dynamodb-refdb
 HA_SITE_PLUGINS_LIBS_LINKS=high-availability
 
-MULTI_SITE_PLUGINS=$(SINGLE_SITE_PLUGINS) multi-site events-kafka websession-broker
+MULTI_SITE_PLUGINS=$(SINGLE_SITE_PLUGINS) multi-site events-kafka websession-broker aws-dynamodb-refdb
 MULTI_SITE_PLUGINS_LIBS_LINKS=multi-site replication
 MULTI_SITE_MAVEN_LIBS=events-broker~$(EVENTSBROKER_LIB_VER)