Fix deprecated section header in keystone.conf

In Icehouse, the [sql] section in keystone.conf has been replaced with
a section called [database] instead to improve consistency across projects.
This patch modifies the puppet-keystone module so that it populates
the [database] section instead of the [sql] section.

Change-Id: I452601cc41d57a78b3390e9516b0b0bef44ceb19
Closes-Bug: #1308861