Some readability fixup for dbconfig

During the backport of the previous patch, Diane Fleming suggested
some fixes: https://review.openstack.org/#/c/97552/. This patch
applies it to the master branch first.

This is a backport of: https://review.openstack.org/97849

Change-Id: I29aca80b836e7730dfd7697f4c90176bc11be8ad