Comment 5 for bug 1747650

Reviewed: https://review.openstack.org/543489
Committed: https://git.openstack.org/cgit/openstack/nova/commit/?id=a564fe1ac260381e786202ec1ea4de903b9cadc0
Submitter: Zuul
Branch: stable/queens

commit a564fe1ac260381e786202ec1ea4de903b9cadc0
Author: Surya Seetharaman <email address hidden>
Date: Tue Feb 6 12:36:50 2018 +0100

    Make bdms querying in multi-cell use scatter-gather and ignore down cell

    This patch makes the querying of bdms from multiple cells in the
    _get_instance_bdms_in_multiple_cells function of extended_volumes use
    scatter_gather_cells thus making the process, parallel. It also adds
    warnings in case a cell is not available; which the operator can later
    tweak, if an exception needs to be raised. So for now, cells that are
    not reachable are ignored and it proceeds to the next cell.

    Change-Id: I0e05eb1e2ad37962968b79100bf4a96c7d6ddd8f
    Closes-Bug: #1747650
    (cherry picked from commit ea6757092df85b6cce38980ae5b7f54b76657e01)