Use database connection for keystone

The keystone configuration used the 'connection' option in the
'sql' section of the keystone.conf file. This option is deprecated
in favor of 'connection' in the 'database' section.

The keystone setup code is changed to use the option in the new
section rather than the deprecated one.

Change-Id: I62fd2f50ded3b8848e9e5225e88c80ed8fed3bff
Merge "Use database connection for keystone"
Merge branch 'master' of https://github.com/openstack-dev/devstack