resize to the same host unexpectedly clears host_info cache

[norman shen]

Description
===========
We are using victoria nova and find that after a same-host-cold-migrate, subsequently cold migrate could break anti-affinity policy.

Steps to reproduce
==================

1 provision a openstack cluster with 2 compute nodes
2 create a server group with anti-affinity rule
3 create two vms binding tot he server group
4 disable compute node B
5 cold migrate server on node A and confirm it
6 right after confirm succeeded, migrate server on node B
7 check vm host if not on the same host , then repeat 5 - 6

Expected result
===============

servers will reside on different nodes

[OpenStack Infra (hudson-openstack)]

Fix proposed to branch: master
Review: https://review.opendev.org/c/openstack/nova/+/866521