spec: fix p2 specs broken by 'take_quiz_button' change

fixes specs broken by g/69582 change.

test plan:
-Specs pass
-code review

Change-Id: I6f304ca2cd29940b12118b3caccd678f299abc7d
Reviewed-on: https://gerrit.instructure.com/71726
Reviewed-by: Deepeeca Soundarrajan <dsoundarrajan@instructure.com>
Tested-by: Jenkins
Product-Review: Matt Fairbourn <mfairbourn@instructure.com>
QA-Review: Matt Fairbourn <mfairbourn@instructure.com>

spec/selenium/quizzes/quizzes_stats_spec.rb

@@ -35,7 +35,7 @@ describe 'quizzes stats' do
         get "/courses/#{@course.id}/quizzes/#{@quiz.id}"
 
         # take the quiz
-        f('#take_quiz_link').click
+        f('#preview_quiz_button').click
         wait_for_ajaximations
         f('#submit_quiz_button').click
         driver.switch_to.alert.accept

spec/selenium/quizzes/varied_due_dates/quizzes_vdd_show_page_ta_spec.rb

@@ -37,8 +37,8 @@ describe 'viewing a quiz with variable due dates on the quiz show page' do
         include_text("#{format_time_for_view(@lock_at_b)}")
     end
 
-    it 'allows taking the quiz', priority: "2", test_id: 282396 do
-      expect(f('.take_quiz_button')).to be_displayed
+    it 'allows previewing the quiz', priority: "2", test_id: 282396 do
+      expect(f('#preview_quiz_button')).to be_displayed
     end
   end
 end