Comment 4 for bug 1705141

Reviewed: https://review.openstack.org/484988
Committed: https://git.openstack.org/cgit/openstack/nova/commit/?id=dcde535f957e2eb4b8bfddd48d6f19eef05ad4f9
Submitter: Jenkins
Branch: master

commit dcde535f957e2eb4b8bfddd48d6f19eef05ad4f9
Author: Matt Riedemann <email address hidden>
Date: Tue Jul 18 20:08:57 2017 -0400

    Handle None returned from get_allocation_candidates due to connect failure

    The get_allocation_candidates method is decorated with the safe_connect
    decorator that handles any failures trying to connect to the Placement
    service. If keystoneauth raises an exception, safe_connect will log it
    and return None. The select_destinations() method in the SchedulerManager
    needs to handle the None case so it doesn't assume a tuple is coming back
    which would result in a TypeError.

    Change-Id: Iffd72f51f25a9e874eaacf374d80794675236ac1
    Closes-Bug: #1705141