'Availability zone' not update after instance migrated to other node

[Eric Xie]

Description
===========
As a admin, i want to live-migrate my instance to one target host
which belongs to another availibility zone. Bug after successful
migration, the avalibility zone is the old one when i show the info
of the instance.

Steps to reproduce
==================
* Create one instance on host1 which belongs to zone1
* Use `nova live-migrate --force ID host1`, host1 belongs to zone2
* Use `nova show ID` to get detailed info

Expected result
===============
The 'availibity zone' should be zone2

Actual result
=============
The 'availibity zone' should be zone1

Environment
===========
1. Exact version of OpenStack you are running. See the following
  list for all releases: http://docs.openstack.org/releases/
# dpkg -l | grep nova
ii nova-api 2:16.1.0-1~u16.04 all OpenStack Compute - compute API frontend
ii nova-common 2:16.1.0-1~u16.04 all OpenStack Compute - common files
ii nova-conductor 2:16.1.0-1~u16.04 all OpenStack Compute - conductor service
ii nova-consoleauth 2:16.1.0-1~u16.04 all OpenStack Compute - Console Authenticator
ii nova-consoleproxy 2:16.1.0-1~u16.04 all OpenStack Compute - NoVNC proxy
ii nova-doc 2:16.1.0-1~u16.04 all OpenStack Compute - documentation
ii nova-placement-api 2:16.1.0-1~u16.04 all OpenStack Compute - placement API frontend
ii nova-scheduler 2:16.1.0-1~u16.04 all OpenStack Compute - virtual machine scheduler
ii python-nova 2:16.1.0-1~u16.04 all OpenStack Compute - libraries
ii python-novaclient 2:9.1.1-1~u16.04 all client library for OpenStack Compute API - Python 2.7

2. Which hypervisor did you use?
Libvirt + KVM

[Matt Riedemann (mriedem)]

I've already got a fix for this:

https://review.openstack.org/#/c/567701/