fix speedGrader spec, ensure right student is visible

Change-Id: I83a165982062f5e4ac8a2309e3cda1d0c95ab89b
Reviewed-on: https://gerrit.instructure.com/5872
Reviewed-by: Bryan Madsen <bryan@instructure.com>
Tested-by: Bryan Madsen <bryan@instructure.com>

Author: ryankshaw

spec/selenium/speed_grader_spec.rb

@@ -27,7 +27,7 @@ def student_submission()
     @course.enroll_user(student_2, "StudentEnrollment", :enrollment_state => 'active')
     submission_2 = @assignment.submit_homework(student_2, :body => 'second student submission text')
 
-    get "/courses/#{@course.id}/gradebook/speed_grader?assignment_id=#{@assignment.id}"
+    get "/courses/#{@course.id}/gradebook/speed_grader?assignment_id=#{@assignment.id}#%7B%22student_id%22%3A#{@submission.student.id}%7D"
 
     #check for assignment text in speedgrader iframe
     keep_trying_until{ driver.find_element(:id, 'speedgrader_iframe') }