Use oslo.db in manila

Use oslo.db library instead of own implementation.

Oslo.db code contains different utils for work with db api, db session,
migrations, test classes for db testing, tools for automatic retry
db.api query if db connection was lost, etc.

Oslo.db code was tested better as it is currently used in many projects,
there will be no need in testing our own implementation.

In many cases our own implementation of work with db duplicates
oslo.db code.

Remove:
- manila/common/sqlalchemyutils.py;
- manila/db/sqlalchemy/utils.py;
- manila/db/sqlalchemy/session.py;
- manila/db/sqlalchemy/migration.py;
- DBError, wrap_db_error, InvalidUnicodeParameter exceptions;
- db_sync, db_version, db_version_control, _find_migrate_repo
function

and replace it with appropriate oslo.db functions.

Add 'joinedload' statement to db queries if necessary.

Fix unit tests, clean up test_migrations.py

Implements bp oslo.db

Change-Id: I48a4da797594cf020f67f78024bd0f86b5abd5ef
Merge "Use oslo.db in manila"