e2e: no extra callbacks

Don't try to callback done on e2e tasks a second time -- ensure that as
soon as the task signals its done, we don't call back to orchestrator
a second time.

Closes #679

Author: laurelnaiad

shared/js/dev-tasks/tasks/e2e.js

@@ -139,11 +139,11 @@ myTasks.push({
 
       var done = function (err) {
         if (!haveClosed) {
+          haveClosed = true;
           err = err && !Error.prototype.isPrototypeOf(err) ?
               new Error(err) :
               null;
           ctx.closeActiveServers(function () { cb(err); });
-          haveClosed = true;
         }
       };