According to the release notes[0], in Mitaka a second database
specifically for the api is required. Flip sync_db_api to being
true by default.
[0] "Nova now requires that two databases are available and configured.
The existing nova database needs no changes, but a new nova_api database
needs to be setup."
http://docs.openstack.org/releasenotes/nova/mitaka.html
Change-Id: Ia5fa8ba70b7ce151e7e904f5e8f94658a98dd295