use_route without monkey patching for engine controller tests

spec_helper.rb

#......  
 #A bunch of spec_helper code....
 Rspec.configure do |config|
  module UseRoutesForControllerTests
    def self.included(base)
      base.class_eval do
        routes { MyEngine::Engine.routes }
      end
    end
  end

  config.include UseRoutesForControllerTests, type: :controller
end
#...