Fixes #18. The init of `Environment` object is broken as backend model are now new Odoo API model.
The result  of function `get_backend` is mapped to a list so we have a list of `backend.Backend` object (not model)
It seems is possible to have correct result using decorator and downgrade keywork but I do not like it.
Fix test in order to have mock that match new API behavior
Merge pull request #19 from nbessi/fix_env_init

Fixes #18. The init of `Environment` object is broken