Use oslo.db sessions

[OpenStack Infra]

https://review.openstack.org/49460
commit 44ceda2816b2cd9a6109b37c0c906f0217a2226e
Author: Brant Knudson <email address hidden>
Date: Sun Dec 15 10:00:41 2013 -0600

    Use oslo.db sessions

    Keystone was using its own keystone.common.sql module for
    database access. oslo-incubator's db.sqlalchemy module provides
    the same or better functionality, so use that instead.

    DocImpact
    - The options that were in the [sql] section are deprecated and
      replaced by options in the [database] section. There are
      also several new options in this section. If database
      configuration is described for another project that uses
      oslo-incubator's db.sqlalchemy module the docs can be shared.

    Part of bp use-common-oslo-db-code

    Change-Id: I25b717d9616e9d31316441ae3671d2f86229c2bf

[Gauvain Pocentek (gpocentek)]

All the documentation uses the [database] section.