add slash to chars to sanitize in gradebook export filename

Courses with slashes in the short name was breaking filenames for some
users. This patchset adds / to the list of characters we substitute
with an underscore.

fixes GRADE-1037

test plan:
 - Have canvas configured to use s3 as a storage backend
 - Create a course with / (a slash) in the name.
 - Export the gradebook for that course
 - Observe that the gradebook export ran and the filename has
   substituted an underscore for the slash in the name

Change-Id: Idfae52acae0d975c7fda92da7a57028ca21539b1
Reviewed-on: https://gerrit.instructure.com/147222
Tested-by: Jenkins
Reviewed-by: Derek Bender <djbender@instructure.com>
Reviewed-by: Adrian Packel <apackel@instructure.com>
QA-Review: Anju Reddy <areddy@instructure.com>
Product-Review: Keith T. Garner <kgarner@instructure.com>

app/controllers/gradebook_csvs_controller.rb

@@ -24,7 +24,7 @@ class GradebookCsvsController < ApplicationController
     if authorized_action(@context, @current_user, [:manage_grades, :view_all_grades])
       current_time = Time.zone.now.strftime('%FT%H%M')
       name = t('grades_filename', "Grades") + "-" + @context.short_name.to_s
-      filename = "#{current_time}_#{name}.csv".gsub(/ /, '_')
+      filename = "#{current_time}_#{name}.csv".gsub(%r{/| }, '_')
 
       csv_options = {
         include_sis_id: @context.grants_any_right?(@current_user, session, :read_sis, :manage_sis),

spec/controllers/gradebook_csvs_controller_spec.rb

@@ -22,7 +22,7 @@ require File.expand_path(File.dirname(__FILE__) + '/../spec_helper')
 describe GradebookCsvsController do
   before :once do
     course_with_teacher active_all: true
-    @course.short_name = "ENG101"
+    @course.short_name = "ENG/ 101"
     @course.save
   end
 
@@ -56,7 +56,7 @@ describe GradebookCsvsController do
       get 'show', params: {course_id: @course.id}, format: :json
       json = json_parse(response.body)
       attachment = Attachment.find(json['attachment_id'])
-      expect(@course.short_name).to eq(File.basename(attachment.filename.split("-").last, ".csv"))
+      expect(File.basename(attachment.filename.split("-").last, ".csv")).to eq("ENG__101")
     end
 
     it "the CSV filename starts with YYYY-MM-DDTHHMM" do