Fix bug introduced in 8600986e635c1b102b66700e0b211ed7a4400d38

Rails.env.test? as added in 8600986e635c1b102b66700e0b211ed7a4400d38 causes an error on my Rails 4rc1 project, as it calls env on Ember::Rails::Railtie instead of the real ::Rails. I also  updated Appraisals to check against the office rails 4.0.0 rc1 and rc5 of ember.