make generated scaffold functional tests work inside API engines

[y-yagi]

Currently, generated scaffold functional tests inside api engine will result in an error.

$ ./bin/rails new bukkits --mountable --api 
$ cd bukkits
$ ./bin/rails g scaffold Todo title:string body:string 
      invoke  active_record
      create    db/migrate/20150809124505_create_bukkits_todos.rb
      create    app/models/bukkits/todo.rb
      invoke    test_unit
      create      test/models/bukkits/todo_test.rb
      create      test/fixtures/bukkits/todos.yml
      invoke  resource_route
       route    resources :todos
      invoke  scaffold_controller
      create    app/controllers/bukkits/todos_controller.rb
      invoke    test_unit
      create      test/controllers/bukkits/todos_controller_test.rb 

$ ./bin/rails t
Run options: --seed 2562

# Running:

.EEEEE

Finished in 0.134508s, 44.6071 runs/s, 7.4345 assertions/s.

  1) Error:
Bukkits::TodosControllerTest#test_should_update_todo:
NoMethodError: undefined method `todos' for #<Bukkits::TodosControllerTest:0x007fa2a00a7ea0>



  2) Error:
Bukkits::TodosControllerTest#test_should_create_todo:
NoMethodError: undefined method `todos' for #<Bukkits::TodosControllerTest:0x007fa2a0874598>



  3) Error:
Bukkits::TodosControllerTest#test_should_destroy_todo:
NoMethodError: undefined method `todos' for #<Bukkits::TodosControllerTest:0x007fa2a0886130>



  4) Error:
Bukkits::TodosControllerTest#test_should_get_index:
NoMethodError: undefined method `todos' for #<Bukkits::TodosControllerTest:0x007fa2a088bcc0>



  5) Error:
Bukkits::TodosControllerTest#test_should_show_todo:
NoMethodError: undefined method `todos' for #<Bukkits::TodosControllerTest:0x007fa2a08898a8>


6 runs, 1 assertions, 0 failures, 5 errors, 0 skips

Failed tests:

bin/rails test /home/yaginuma/program/rails/master/bukkits/test/controllers/bukkits/todos_controller_test.rb:27
bin/rails test /home/yaginuma/program/rails/master/bukkits/test/controllers/bukkits/todos_controller_test.rb:14
bin/rails test /home/yaginuma/program/rails/master/bukkits/test/controllers/bukkits/todos_controller_test.rb:32
bin/rails test /home/yaginuma/program/rails/master/bukkits/test/controllers/bukkits/todos_controller_test.rb:9
bin/rails test /home/yaginuma/program/rails/master/bukkits/test/controllers/bukkits/todos_controller_test.rb:22 

This commit fixes so that the test that is generated to work properly.