Comment 0 for bug 1890244

Description
===========
We created a server group and started some instances in it.

Later we removed the server group.

Some time later, we had to evacuate these instances, but this failed, because the
scheduler removed all available hosts during filtering.

Steps to reproduce
==================
* create a server group
* start some instances in this group
* delete the server group
* ( hard poweroff your hypervisor )
* evacuate the instances

Expected result
===============
The instances are evacuated

Actual result
=============
The instances run into ERROR-state, because the server group is not found.

Environment
===========
* Kolla deployed OpenStack Train
* Ubuntu 18.04 / KVM + Libvirt

Logs & Configs
==============

scheduler tells:

 Filtering removed all hosts for the request with instance ID 'adddf2c9-0252-4463-a97c-f1ec209d9f49'. Filter results: ['AvailabilityZoneFilter: (start: 2, end: 2)', 'ComputeFilter: (start: 2, end: 2)', 'ComputeCapabilitiesFilter: (start: 2, end: 2)', 'ImagePropertiesFilter: (start: 2, end: 2)', 'ServerGroupAntiAffinityFilter: (start: 2, end: 2)', 'ServerGroupAffinityFilter: (start: 2, end: 0)']

instance show:

 | fault | {'code': 404, 'created': '2020-08-04T06:13:41Z', 'message': 'Instance group 7e84dc57-de05-4c92-9e3b-6e2d06c1d85b could not be found.'} |