Comment 9 for bug 1718455

Reviewed: https://review.openstack.org/508591
Committed: https://git.openstack.org/cgit/openstack/nova/commit/?id=b97c433f7c24615a81a1342e75fd42fe3c15e3d4
Submitter: Jenkins
Branch: stable/pike

commit b97c433f7c24615a81a1342e75fd42fe3c15e3d4
Author: Sylvain Bauza <email address hidden>
Date: Thu Sep 21 10:52:46 2017 +0200

    Ensure instance can migrate when launched concurrently

    When we fixed the problem in If7da79356174be57481ef246618221e3b2ff8200
    we forgot to modify a specific check in select_destinations().

    Since _schedule() is returning the correct number of needed hosts but
    we were still using the wrong number of instances to verify, the
    conditional in select_destinations() was always incorrect.

    Note that we needed to modify test.py and fake driver because:

     - _do_check_can_live_migrate_destination was using CONF.host
     - check_can_live_migrate_destination in the fake driver was
       incorrectly trying to set a None value to the object while
       libvirt fixed that earlier (block_migration=None when the
       user specifies block_migration='auto' in the API)
     - pre_live_migration in the fake driver was not returning
       migrate_data, which is passed through live_migration and
       _post_live_migration to set the migration object status

    Change-Id: Iff839f3478ebe77bf3e2c4becbe9b9b62fff5035
    Closes-Bug: #1718455
    (cherry picked from commit 87ca0d8af0d6440a7effd4da9e47321b3a335442)