Fix searchlight nova resources indexation

* nova_server resources resources are not actually
indexed.

* nova flavor are not indexed too, cause the notifications topic for
flavors is versioned_notifications.
We need to config notifications_topics_exchanges with value
'versioned_notifications,nova' in order to get the related versioned.

Change-Id: Ibf4ee7d7efceee5aefac5f83e22b994ae33ce047
Closes-Bug: #1703435