add late and missing flags to submission_* live events

fixes DIG-1417
flag=none

test plan:
 - trigger a `submission_updated` live event by submitting an
   assignment.
 - if you submitted on time, the event should contain `"late": false`.
   if it was late, the event should contain `"late": true`.

Change-Id: I856b2748c8cd583308e89f5160e734bc9f287e3c
Reviewed-on: https://gerrit.instructure.com/c/canvas-lms/+/222297
Tested-by: Service Cloud Jenkins <svc.cloudjenkins@instructure.com>
QA-Review: Tucker Mcknight <tmcknight@instructure.com>
Product-Review: Michael Ziwisky <mziwisky@instructure.com>
Reviewed-by: Weston Dransfield <wdransfield@instructure.com>

lib/canvas/live_events.rb

@@ -295,6 +295,8 @@ module Canvas::LiveEvents
       body: LiveEvents.truncate(submission.body),
       url: submission.url,
       attempt: submission.attempt,
+      late: submission.late?,
+      missing: submission.missing?,
       lti_assignment_id: submission.assignment.lti_context_id,
       group_id: submission.group_id
     }

spec/lib/canvas/live_events_spec.rb

@@ -551,6 +551,17 @@ describe Canvas::LiveEvents do
           ))
         Canvas::LiveEvents.submission_updated(submission)
       end
+
+      it 'should include late and missing flags' do
+        submission.update_attributes(late_policy_status: 'missing')
+
+        expect_event('submission_updated',
+          hash_including(
+            late: false,
+            missing: true
+          ))
+        Canvas::LiveEvents.submission_updated(submission)
+      end
     end