Install Guide: Setup first config files, then run openstack-db

Change-Id: I778c246bcb3fbb89bc31f4b52861813619baf759
Backport: stable/havana
Cherry-Pick: https://review.openstack.org/#/c/52896/
Closes-Bug: #1242602
Merge "Install Guide: Setup first config files, then run openstack-db" into stable/havana