Add support to oslo.db to be used as a DB driver. The DB driver will be
used with API v2. When it's completely implemented, API V1 will be
deprecated and removed by the end of the cycle. Freezer-api will keep
supporting V2 with Elasticsearch, Sqlalchemy drivers.
This patch implements the follow:
* Abstract Base DB driver to be implemented by each driver
* Base driver; will return only access to the db engine, session
* SqlAlchemy driver;
* ElasticSearch driver;
* Implement both drivers in freezer-manage
Partially-Implements: blueprint oslo-db
Depends-On: I81e417155da48f46dd2113e5745fb3c21c96499f
Depends-On: I2e5724b1f1a75121952e2beb3844d2c489e4df68
Depends-On: Idb4ac050652d1d0107bf3fcd447d7cbedd811809
Depends-On: I81d46c89859752c0cbc21ef02de90db7f19f942c
Change-Id: I93ed1b909f538728a1a9bd5c8b07baf7aeddb705