Fix raise error when query datasource

[roganw]

Optimize the code by changing the db.session.query()... method to call get_datasource().
And fix the error in line: 1056 and line: 2003, query using one(), which will raise sqlalchemy.orm.exc.NoResultFound if the query selects no rows.

[coveralls]

Coverage decreased (-0.009%) to 69.41% when pulling bd48a9c on RoganW:fix_datasource_raise_error into 232a5c3 on apache:master.