Fix AZ List Detail schema to allow hosts as None

[Ghanshyam Mann]

List AZ with Details response can return host as None for non available AZ from nova.

But response schema [1] always expect host as non None value which is not true for non available AZ on nova side.

..1 https://github.com/openstack/tempest/blob/master/tempest/lib/api_schema/response/compute/v2_1/availability_zone.py#L54

ref- https://github.com/openstack/nova/blob/master/nova/api/openstack/compute/availability_zone.py#L102

[OpenStack Infra (hudson-openstack)]

Fix proposed to branch: master
Review: https://review.openstack.org/430590

[Ghanshyam Mann (ghanshyammann)]

failure log - http://logs.openstack.org/03/430403/2/check/gate-tempest-dsvm-neutron-dvr-ubuntu-xenial/dbf0c3c/logs/testr_results.html.gz

[OpenStack Infra (hudson-openstack)]

Reviewed: https://review.openstack.org/430590
Committed: https://git.openstack.org/cgit/openstack/tempest/commit/?id=77b3eb15b1049785bbfce1ef4f1a06c7e4c01265
Submitter: Jenkins
Branch: master

commit 77b3eb15b1049785bbfce1ef4f1a06c7e4c01265
Author: ghanshyam <email address hidden>
Date: Wed Feb 8 06:53:42 2017 +0000

    Fix AZ List Detail schema to allow hosts as None

    List AZ with Details response can return host as None
    for non available AZ from nova.

    But response schema [1] always expect host as non-None
    value which is not true for non available AZ on nova side.

    Change-Id: I015ea26eb47ef179d55f3e452e871bfeec406365
    Closes-Bug: #1662781