Add retry loop to delegate_email for getting CourseEmail

Revert hardcoded delay for course_email task

lms/djangoapps/bulk_email/tasks.py

@@ -37,6 +37,19 @@ def delegate_email_batches(hash_for_msg, recipient, course_id, course_url, user_
         log.error("get_course_by_id failed: " + exc.args[0])
         raise Exception("get_course_by_id failed: " + exc.args[0])
 
+    email = None
+    retries = 0
+    while email is None:
+        try:
+            email = CourseEmail.objects.get(hash=hash_for_msg)        
+        except CourseEmail.DoesNotExist as exc:
+            if retries < 3:
+                retries += 1
+                time.sleep(5)
+            else:
+                log.error("Failed to get CourseEmail with hash " + hash_for_msg + ", no workers fired.")
+                return 0
+
     if recipient == "myself":
         recipient_qset = User.objects.filter(id=user_id).values('profile__name', 'email')
     else:
@@ -63,7 +76,7 @@ def delegate_email_batches(hash_for_msg, recipient, course_id, course_url, user_
 
     for i in range(num_workers):
         to_list = recipient_list[i * chunk:i * chunk + chunk]
-        course_email.apply_async(args=[hash_for_msg, to_list, course.display_name, course_url, False], countdown=10)
+        course_email.delay(hash_for_msg, to_list, course.display_name, course_url, False)
     return num_workers