Comment 4 for bug 1827492

Reviewed: https://review.opendev.org/659703
Committed: https://git.openstack.org/cgit/openstack/nova/commit/?id=2af89cfea0531ab75b4f5765bb220073f42662d0
Submitter: Zuul
Branch: master

commit 2af89cfea0531ab75b4f5765bb220073f42662d0
Author: pandatt <guojy8993@163.com>
Date: Thu May 16 02:50:57 2019 +0800

    Skip existing VMs when hosts apply force_config_drive

    When hosts apply config `CONF.force_config_drive=True`, the existing
    VMs shouldn't be enforced to must have config drive device. For they
    may have been cloud-inited via metadata service, and may not need and
    have any config drive device ever. In contrast, the newly being-built
    ones should. Instance attr `launched_at` serves as an apparent flag
    to distinguish the two kinds of VMs.

    When hard reboots happend, existing VMs skip config drive enforcement,
    and therefore avoid hitting 'No such file or directory (config drive
    device)' error.

    Change-Id: I0558ece92f8657c2f6294e07965c619eb7c8dfcf
    Closes-Bug: #1827492