Handle batched reads from cloned sessions

Readwritesplit should route all queries from cloned sessions to the
master. This allows batch statements to be safely routed.

Native readwritesplit sessions only support batched writes as batched
reads aren't very common. Once readwritesplit supports batched reads, the
special handling for cloned DCBs can be removed.

server/modules/routing/readwritesplit/rwsplit_route_stmt.c

@@ -696,6 +696,13 @@ route_target_t get_route_target(ROUTER_CLIENT_SES *rses,
     {
         target = TARGET_MASTER;
     }
+    /**
+     * A cloned session, route everything to the master
+     */
+    else if (DCB_IS_CLONE(rses->client_dcb))
+    {
+        target = TARGET_MASTER;
+    }
     /**
      * These queries are not affected by hints
      */