In I12a02f636f31985bc1b71bff5b744d346286a95f cell_v2 discovery was
originally moved from the nova-api container to the
nova-compute|nova-ironic containers in order to run cell
discovery during a scale up where the controllers are omitted
(e.g to exclude the controllers from a maintenance window).
This requires api database credentials on the compute node, which is
forbidden, so it must move back to a nova-api host as a pre-requisite
for removing these credentials in a follow-up patch.
Scale-up while omitting the controllers will no longer work out of the
box. Either a manual cell_v2 discovery can be run after scale up, or an
additional node can be deployed using the NovaManager tripleo role.
(cherry picked from commit 629485dde5)
(cherry picked from commit 03697234fd)