Add DB utils from Oslo

There is a lot of work done around DB and sqlalachemy in OSLO:

1) session and egnine wrappers
2) base models
3) tests for migration on real backends
4) exception wrappers
5) provide work around unqiue constraints
...
Add base for DB API

Add DB API layer:
*) create, drop table methods
*) DB API interface layer
*) DB API sqlalchemy implementation

Add DB Models layer:
*) Base Model
*) Create Drop Table by models

Add common oslo wrappers to add 2 new class:
1) TestCase - with DB Fixture
2) NoDBTestCase - without DB Fixture

Add base exceptions
Add Task Model

Add CRUD method for Task Model

Add Tests for this model

Add consts status for this model

Add TaskNotFound exception