Manual submission close to the time-limit display as multiple submissions

flag=none

closes QO-354

test plan:
- create a timed classic quiz
- after time is up, close the alert box
- see "Submit Quiz" button is disabled

Change-Id: Ibfc16564e5e94dff3e0fc258a52189e7483f9a88
Reviewed-on: https://gerrit.instructure.com/c/canvas-lms/+/233766
Tested-by: Service Cloud Jenkins <svc.cloudjenkins@instructure.com>
Reviewed-by: Vidya Subramaniam <vsubramaniam@instructure.com>
Reviewed-by: Jim Simon <jsimon@instructure.com>
QA-Review: David Tan <dtan@instructure.com>
Product-Review: Kevin Dougherty <jdougherty@instructure.com>

public/javascripts/take_quiz.js

@@ -465,7 +465,9 @@ var quizSubmission = (function() {
         .removeClass(removeClass)
     },
     submitQuiz() {
-      const action = $('#submit_quiz_button').data('action')
+      const button = $('#submit_quiz_button')
+      button.prop('disabled', true)
+      const action = button.data('action')
       $('#submit_quiz_form')
         .attr('action', action)
         .submit()