ocata: cell host discovery is racey

[James Page]

For ocata, use of a single cell is required and the "nova-manage cell_v2 discover_hosts" must be run at suitable points in time during deployment to ensure that compute hosts get mapped into the correct cell in the nova_api database.

Without re-designing the relation semantics between nova-compute and nova-cloud-controller this is hard to achieve.

As a interim measure, we can enable the option that performs periodic host discovery in the scheduler, with a longer term plan to be able to disable this for larger deployments, and use an action to allow the operator to determine when new compute hosts are mapped into cells for use.

This will require that compute service come up disabled by default - they can then be enabled as part of this activity.

[James Page (james-page)]

https://review.openstack.org/#/c/437162/

[OpenStack Infra (hudson-openstack)]

Reviewed: https://review.openstack.org/437162
Committed: https://git.openstack.org/cgit/openstack/charm-nova-cloud-controller/commit/?id=98459797bb6758e9a0d49895b9571474fc8227fb
Submitter: Jenkins
Branch: master

commit 98459797bb6758e9a0d49895b9571474fc8227fb
Author: James Page <email address hidden>
Date: Wed Feb 22 16:48:46 2017 -0500

    Enable automatic host cell discovery

    Configure the scheduler to automatically discover and
    map hosts into cell1 every 30 seconds ensuring that
    hosts are discovered automatically.

    This will be completed by future work to orchestrate
    the enablement and mapping of compute hosts into cells
    using relations and actions at a later date.

    Change-Id: I5ed10e67936388bb074739b63e3a5ecf9036035f
    Partial-Bug: 1667124