billing: integration test creating customer
billing: fix integration test

This actually required three little fixes:
* couchrest_session_store updated to 0.1.2 to make sure we store sessions
* use BraintreeTestApp to proxy braintree requests that RackTest assumes
  are local
* do not attempt to read status after a capybara request

Also refactored the test a bit to set @user and login during setup.