Don't disable compute cell in scale down tasks for additional cells

When we scale down a compute in an additional cell, disabling the compute
service fails in scale down tasks as the workflow of scale down a compute
from an additional cell is [1]:

- migrate off instances from the compute or delete them
- remove the compute from the cell (nova-manage command)
- scale down the cell stack

Until we have fully automated scale down of a compute from an additional
cell, don't run disable of compute service as we have already removed it from
cell in pre steps.

[1] https://docs.openstack.org/project-deploy-guide/tripleo-docs/latest/features/deploy_cellv2_manage_cell.html#delete-a-compute-from-a-cell

Change-Id: Ie699d7d3367652f4a4dfcb5bf7e52b81c4325aae
Closes-Bug: #1859825

deployment/nova/nova-compute-container-puppet.yaml

@@ -1083,6 +1083,9 @@ outputs:
               delegate_to: localhost
               check_mode: no
               changed_when: false
+            - name: is additional Cell?
+              set_fact:
+                is_additional_cell: {get_param: NovaAdditionalCell}
             - name: Set fact for nova_compute services
               set_fact:
                 nova_compute_service: "{{ nova_compute_service_result.stdout | from_yaml | selectattr('Host', 'match', ansible_fqdn ~ '.*') | list }}"
@@ -1105,6 +1108,7 @@ outputs:
               check_mode: no
               when:
                 - (nova_compute_service | length) <= 1
+                - not is_additional_cell|bool
             - name: Stop nova-compute healthcheck container
               service:
                 name: tripleo_nova_compute_healthcheck