Comment 7 for bug 1754360

Reviewed: https://review.openstack.org/581451
Committed: https://git.openstack.org/cgit/openstack/nova/commit/?id=bcae081c4672a13eb1a75d1d3d81a439b5fdb796
Submitter: Zuul
Branch: stable/queens

commit bcae081c4672a13eb1a75d1d3d81a439b5fdb796
Author: Eric M Gonzalez <email address hidden>
Date: Thu Mar 8 09:11:25 2018 -0600

    unquiesce instance after quiesce failure

    If the call to compute_rpcapi.quisece_instance() raises an exception,
    any uncaught exception will break out of the function
    snapshot_volume_backed(). This can leave the instance in frozen state.

    This patch adds a blanket Exception catch to the try block and calls
    compute_rpcapi.unquiesce_instance() before reraising.

    This has been seen in the wild with RPC timeouts, but this is not the
    only possible genesis for an unknown error from quiesce_instance.

    Change-Id: Idca5998da8bb42b29a8fffdf52b4af3a043c6326
    Closes-Bug: #1754360
    (cherry picked from commit 1e77faaa412ab9909dd9491cab4a819b5c84d3e8)