Description of problem:

Instance creation is getting failed after setting hw:cpu_thread_policy as isolate
Here is the output of openstack flavor show:

~~~
+----------------------------+------------------------------------------------------------------------------------------------+
| Field                      | Value                                                                                          |
+----------------------------+------------------------------------------------------------------------------------------------+
| OS-FLV-DISABLED:disabled   | False                                                                                          |
| OS-FLV-EXT-DATA:ephemeral  | 0                                                                                              |
| access_project_ids         | None                                                                                           |
| description                | None                                                                                           |
| disk                       | 30                                                                                             |
| extra_specs                | {'hw:cpu_policy': 'dedicated', 'hw:cpu_thread_policy': 'isolate', 'hw:mem_page_size': 'large'} |
| id                         | 296b5673-7f3d-4cf7-94fc-2013321b5641                                                           |
| name                       | test-sriov-isolates-thread                                                                     |
| os-flavor-access:is_public | True                                                                                           |
| properties                 | hw:cpu_policy='dedicated', hw:cpu_thread_policy='isolate', hw:mem_page_size='large'            |
| ram                        | 16384                                                                                          |
| rxtx_factor                | 1.0                                                                                            |
| swap                       | 0                                                                                              |
| vcpus                      | 8                                                                                              |
+----------------------------+------------------------------------------------------------------------------------------------+
~~~


Version-Release number of selected component (if applicable):
 installed-rpms |grep nova
puppet-nova-15.5.1-0.20200608173427.c15e37c.el8ost.noarch   Tue Aug  4 14:04:37 2020
python3-novaclient-15.1.0-0.20200310162625.cd396b8.el8ost.noarch Tue Aug  4 14:05:55 2020


How reproducible:
spawn the instance with same flavor on 16 and it went into error state

Steps to Reproduce:
1.
2.
3.

Actual results:
Instance went into error state

Expected results:
Instance should spawn successfully

Additional info:
It was working in osp13