Fix missed created_at and replace it with client_timestamp

fixes CNVS-26913

test plan
- Create a quiz and add a question of any type to the quiz.
- Open the quiz in safari as a student.
- Ensure that the quiz loads correctly

Change-Id: I31aecfd63f5753aaa0251377371a732b603a8481
Reviewed-on: https://gerrit.instructure.com/71164
Reviewed-by: Josh Simpson <jsimpson@instructure.com>
QA-Review: Deepeeca Soundarrajan <dsoundarrajan@instructure.com>
Tested-by: Jenkins
Product-Review: Davis McClellan <dmcclellan@instructure.com>

app/coffeescripts/quizzes/log_auditing/event.coffee

@@ -8,7 +8,7 @@ define (require) ->
     # @internal Create an Event from the JSON version stored in localStorage.
     @fromJSON: (descriptor) ->
       event = new QuizEvent(descriptor.event_type, descriptor.event_data)
-      event.recordedAt = new Date(descriptor.created_at)
+      event.recordedAt = new Date(descriptor.client_timestamp)
       event
 
     constructor: (type, data) ->
@@ -54,4 +54,4 @@ define (require) ->
       }
 
     toString: ->
-      JSON.stringify(this.toJSON())
+      JSON.stringify(this.toJSON())

spec/coffeescripts/quizzes/log_auditing/event_spec.coffee

@@ -18,7 +18,7 @@ define [
 
   test 'QuizEvent.fromJSON', ->
     descriptor = {
-      created_at: (new Date()).toJSON(),
+      client_timestamp: (new Date()).toJSON(),
       event_type: 'some_type',
       event_data: {
         foo: 'bar'
@@ -26,6 +26,7 @@ define [
     }
 
     event = QuizEvent.fromJSON(descriptor)
+    ok (event.recorded_at == descriptor.client_timestamp)
 
     equal event.type, descriptor.event_type,
       'it parses the type'
@@ -34,4 +35,4 @@ define [
       'it parses the custom data'
 
     deepEqual event.recordedAt, new Date(descriptor.created_at),
-      'it parses the recording timestamp'
+      'it parses the recording timestamp'