Periodic spec failure in spec/features/boards/boards_spec.rb

@rdavila and I have seen this spec to fail over the last weekend:

https://gitlab.com/gitlab-org/gitlab-ce/builds/3317757

 1) Issue Boards with lists filtering filters by multiple labels
     Failure/Error: @list ||= board.lists.find(params[:id])

     NoMethodError:
       undefined method `lists' for nil:NilClass
     # ./app/services/boards/issues/list_service.rb:14:in `list'
     # ./app/services/boards/issues/list_service.rb:39:in `set_state'
     # ./app/services/boards/issues/list_service.rb:21:in `filter_params'
     # ./app/services/boards/issues/list_service.rb:5:in `execute'
     # ./app/controllers/projects/boards/issues_controller.rb:8:in `index'
     # ./lib/gitlab/request_profiler/middleware.rb:15:in `call'
     # ./lib/gitlab/middleware/go.rb:16:in `call'
     # ./lib/gitlab/middleware/static.rb:9:in `call'