Session does not use ceilometer.conf's database_connection

use [database]connection setting from openstack.common sqlalchemy session

Change-Id: I582d4cb7d51d6ddecc27ae5fcdedcfd19dc898af
Fixes: bug #1183106
Start to use Hacking

Instead of ignoring all Hacking warnings, blacklist
those that need lots of changes and fix the easy one.

Change-Id: I0a31982b1ff17c54e1347bff5358bb9f8e637b6f
Merge "Start to use Hacking"