Sync db code from oslo-incubator

Sync db code from oslo-incubator

Synced from commit 5fb343faee1442921e2d610b1a5222e67418c4cd.
Due to changes in oslo.db API, this sync requires a bit more
work on Neutron side.

Sync includes the following commits:

5b7e61c Dispose db connections pool on disconnect
d1988b9 Set sql_mode callback on connect instead of checkout
a1a8280 Fix excessive logging from db.sqlalchemy.session
9933bdd Get mysql_sql_mode parameter from config
96a2217 Prevent incorrect usage of _wrap_db_error()
20a7510 Add from_config() method to EngineFacade
fea119e Drop special case for MySQL traditional mode, update unit tests
dda24eb Introduce mysql_sql_mode option, remove old warning
0b5af67 Introduce a method to set any MySQL session SQL mode
8dccc7b Handle ibm_db_sa DBDuplicateEntry integrity errors
5b9e9f4 Fix doc build errors in db.sqlalchemy
ac84a40 Update log translation domains
86707cd Remove None for dict.get()
0545121 Fix duplicating of SQL queries in logs
fcf517d Update oslo log messages with translation domains
630d395 Don't use cfg.CONF in oslo.db
ce69e7f Don't store engine instances in oslo.db

Change-Id: I0e1d86878d3eb924b01e04dced0f90b4e57757d8