Comment 4 for bug 1809136

Reviewed: https://review.openstack.org/626410
Committed: https://git.openstack.org/cgit/openstack/nova/commit/?id=bc0a5d0355311641daa87b46e311ae101f1817ad
Submitter: Zuul
Branch: stable/rocky

commit bc0a5d0355311641daa87b46e311ae101f1817ad
Author: Stephen Finucane <email address hidden>
Date: Wed Dec 19 16:03:22 2018 +0000

    Handle unbound vif plug errors on compute restart

    As with change Ia963a093a1b26d90b4de2e8fc623031cf175aece, we can
    sometimes cache failed port binding information which we'll see on
    startup. Long term, the fix for both issues is to figure out how this is
    being cached and stop that happening but for now we simply need to allow
    the service to start up.

    To this end, we copy the approach in the aforementioned change and
    implement a translation function in os_vif_util for unbound which
    will make the plug_vifs code raise VirtualInterfacePlugException which
    is what the _init_instance code in ComputeManager is already handling.

    This has the same caveats as that change, namely that there may be
    smarter ways to do this that we should explore. However, that change
    also included a note which goes someway to explaining this.

    Change-Id: Iaec1f6fd12dba8b11991b7a7595593d5c8b1db50
    Signed-off-by: Stephen Finucane <email address hidden>
    Related-bug: #1784579
    Closes-bug: #1809136
    (cherry picked from commit 1def76a1c49032d93ab6c7ee61dbbfe8e29cafca)