DB queries log entries are duplicated

In oslo.db we can enable logging of DB queries by the means of CONF.database.connection_debug options. It's implemented by passing of echo=True/'debug' to SQLAlchemy create_engine() factory function, which internally calls logging.basicConfig(), that adds handler to the root logger.

But we also set up handlers for the root logger in openstack.common.log setup() function. This results in attaching of two handlers writing entries to stderr to the root logger. And it's clearly stated in SQLAlchemy docs: "...when using Python logging, ensure all echo flags are set to False at all times, to avoid getting duplicate log lines."(http://docs.sqlalchemy.org/en/rel_0_9/core/engines.html#dbengine-logging)

To fix this we need to stop passing echo=True to create_engine() in oslo.db and replace it with setting the correct log level directly on the logger (in this case it's 'sqlalchemy.engine').

Snippet to reproduce (it's not using oslo code, but effectively behaves the same way):

import logging

import sqlalchemy as sa

# this is a simplified version of what we are doing in openstack.common.log
root = logging.getLogger()
root.addHandler(logging.StreamHandler())

# log entries of DB queries are duplicated
eng = sa.create_engine('sqlite://', echo=True)
eng.execute('select 1;')