Comment 12 for bug 1731986

Reviewed: https://review.openstack.org/545961
Committed: https://git.openstack.org/cgit/openstack/nova/commit/?id=7ab98b5345f4a023bd209e714cd0aa60b3a31d48
Submitter: Zuul
Branch: stable/queens

commit 7ab98b5345f4a023bd209e714cd0aa60b3a31d48
Author: Eric M Gonzalez <email address hidden>
Date: Mon Nov 13 14:02:27 2017 -0600

    unquiesce instance on volume snapshot failure

    This patch adds an exception catch to "snapshot_volume_backed()" of
    compute/api.py that catches (at the moment) _all_ exceptions from the
    underlying cinderclient. Previously, if the instance is quiesced ( frozen
    filesystem ) then the exception will break execution of the function,
    skipping the needed unquiesce, and leave the instance in a frozen state.

    Now, the exception catch will unquiesce the instance if it was prior to
    the failure.

    Got a unit test in place with the help of Matt Riedemann.
        test_snapshot_volume_backed_with_quiesce_create_snap_fails

    Change-Id: I60de179c72eede6746696f29462ee9d805dace47
    Closes-bug: #1731986
    (cherry picked from commit bca425a33f52584051348a3ace832be8151299a7)