Comment 4 for bug 1869371

Reviewed: https://review.opendev.org/720518
Committed: https://git.openstack.org/cgit/openstack/kolla-ansible/commit/?id=5ac8d6224ba4e9f721a5f1a45fea454318afe443
Submitter: Zuul
Branch: stable/train

commit 5ac8d6224ba4e9f721a5f1a45fea454318afe443
Author: Mark Goddard <email address hidden>
Date: Fri Mar 27 13:27:15 2020 +0000

    Fix nova compute addition with limit

    Deploy a small cloud. Add one host to the compute group in the
    inventory, and scale out:

    $ kolla-ansible deploy --limit <new compute host>

    The command succeeds, but creating an instance fails with the following:

        Host 'compute0' is not mapped to any cell

    This happens because we only discover computes on the first host in the
    cell's nova conductor group. If that host is not in the specified limit,
    the discovery will not happen.

    This change fixes the issue by running compute discovery when any ironic
    or virtualised compute hosts are in the play batch, and delegating it to
    a conductor.

    Change-Id: Ie984806240d147add825ffa8446ae6ff55ca4814
    Closes-Bug: #1869371
    (cherry picked from commit 3af28d2151f9e3431e81e5d23e0e2a72cea2c034)