Setup test db

I changed the py.test session setup/teardown functions to clean the db between every test run. You can find in test_setup.py an example of test that uses py.test fixtures to create the initial database. 
The project_job and project_objectstore databases can be created adding a new datasource to the db. This can be done from the admin too, since the db creation/deletion is hooked to the delete/save methods of Datasource