Originality score pass back works again

Fixes PLAT-1771

Test Plan:
Create a TII assignment, submit it as a student
see that the originality score is visible in canvas itself

Change-Id: Ifab2590ba2333d7a5b3a991cbf5ca7e0b96f026f
Reviewed-on: https://gerrit.instructure.com/88583
Reviewed-by: Nathan Mills <nathanm@instructure.com>
Tested-by: Jenkins
QA-Review: August Thornton <august@instructure.com>
Product-Review: Matthew Wheeler <mwheeler@instructure.com>

lib/turnitin/outcome_response_processor.rb

@@ -71,10 +71,10 @@ module Turnitin
     private
 
     def stash
-      old_turnit_client = @turnitin_client
-      @turnitin_client = nil
+      old_turnit_client = @_turnitin_client
+      @_turnitin_client = nil
       yield
-      @turnitin_client = old_turnit_client
+      @_turnitin_client = old_turnit_client
     end
 
     def attempt_number