Extra tests for html, xml, json and tail nodes

(and some consistent passing of missing payloads)

nodes/core/storage/28-tail.js

@@ -61,6 +61,7 @@ module.exports = function(RED) {
         });
 
         this.on("close", function() {
+            /* istanbul ignore else */
             if (tail) { tail.kill(); }
         });
     }