Add log statement

Author: MarcialRosales

deps/rabbitmq_auth_backend_cache/src/rabbit_auth_backend_cache.erl

@@ -68,6 +68,7 @@ expiry_timestamp(_) -> never.
 
 clear_cache_cluster_wide() ->
     Nodes = rabbit_nodes:list_running(),
+    rabbit_log:warning("Clearing auth_backend_cache in all nodes : ~p", [Nodes]),
     rabbit_misc:append_rpc_all_nodes(Nodes, ?MODULE, clear_cache, []).
 
 clear_cache() ->