`openstack hypervisor list` shows `down` state even when the hypervisors are all up

Issue

• openstack hypervisor list shows down state even when the hypervisors are all up:

(undercloud) [stack@director ~]$ nova service-list
+--------------------------------------+----------------+-----------+----------+---------+-------+----------------------------+-----------------+-------------+
| Id                                   | Binary         | Host      | Zone     | Status  | State | Updated_at                 | Disabled Reason | Forced down |
+--------------------------------------+----------------+-----------+----------+---------+-------+----------------------------+-----------------+-------------+
| e90995c6-5ea4-479d-8a99-e0c45c6e202e | nova-conductor | director | internal | enabled | down  | 2019-01-21T00:55:25.000000 | -               | False       |
| 4cbede78-cd40-41ea-a0fb-57605a663ef9 | nova-scheduler | director | internal | enabled | down  | 2019-01-21T00:55:29.000000 | -               | False       |
| 899952fc-1d8d-4ccc-932c-9689679a24d2 | nova-compute   | director | nova     | enabled | down  | 2019-01-21T00:55:28.000000 | -               | False       |
| 6f8c685b-cc49-4222-baea-915b42c9e75f | nova-conductor | director | internal | enabled | up    | 2019-12-05T13:34:46.000000 | -               | False       |
| ba3e5f4f-5ada-48ef-9e83-bb9f6474f19a | nova-scheduler | director | internal | enabled | up    | 2019-12-05T13:34:46.000000 | -               | False       |
| 18411a28-6260-4766-aa77-0b304750d54a | nova-compute   | director | nova     | enabled | up    | 2019-12-05T13:34:46.000000 | -               | False       |
+--------------------------------------+----------------+-----------+----------+---------+-------+----------------------------+-----------------+-------------+

• In the State column of openstack hypervisor list, the host is down:

(undercloud) [stack@director ~]$ openstack hypervisor list
+----+--------------------------------------+-----------------+-----------+-------+
| ID | Hypervisor Hostname                  | Hypervisor Type | Host IP   | State |
+----+--------------------------------------+-----------------+-----------+-------+
|  1 | c2602fe6-91a5-4f5c-8d3d-6478637e7b33 | ironic          | 127.0.0.1 | down  |
|  2 | 754ee86a-465d-46cd-9f82-1234df75237b | ironic          | 127.0.0.1 | down  |
|  3 | e2bd393d-c94b-4d4a-a6da-c1eb4ebffa05 | ironic          | 127.0.0.1 | down  |
|  4 | 6327e831-25ee-496a-8aa8-552308f48585 | ironic          | 127.0.0.1 | down  |
|  5 | 122d799e-1c1a-4faa-9f9f-b80162ef71f2 | ironic          | 127.0.0.1 | down  |
|  6 | 8d3fa213-3bc5-4aff-9588-49069a712833 | ironic          | 127.0.0.1 | down  |
|  7 | 9b20c9b6-0021-4f3d-88db-d221c87861fb | ironic          | 127.0.0.1 | down  |
+----+--------------------------------------+-----------------+-----------+-------+