Run nova_cell_v2_discover_hosts.py on every deploy run

Change I1a159a7c2ac286373df2b7c566426b37b7734961 moved the dicovery
to run on a single compute host to not race on simultanious nova-manage
commands. This change make sure we run the discover on every deploy run
which is required for scaling up events.

Change-Id: Iba7a4aeeeeb94ffbbaf4bb757672091807301494
Related-bug: 1824445
(cherry picked from commit dfc99bad08)
(cherry picked from commit 2c07850699)

docker/services/nova-compute.yaml

@@ -291,6 +291,13 @@ outputs:
                   - /var/lib/docker-config-scripts/:/docker-config-scripts/
             user: root
             command: "su nova -s /bin/bash -c '/docker-config-scripts/nova_cell_v2_discover_hosts.py'"
+            environment:
+              # NOTE: this should force this container to re-run on each
+              # update (scale-out, etc.)
+              - list_join:
+                  - ''
+                  - - 'TRIPLEO_DEPLOY_IDENTIFIER='
+                    - {get_param: DeployIdentifier}
       host_prep_tasks:
         list_concat:
         - {get_attr: [NovaLogging, host_prep_tasks]}

releasenotes/notes/nova_run_cell_discovery_on_each_run-11dbb6096ebbf51b.yaml

@@ -0,0 +1,7 @@
+---
+fixes:
+  - |
+    Change-Id: I1a159a7c2ac286373df2b7c566426b37b7734961 moved the dicovery
+    to run on a single compute host to not race on simultanious nova-manage
+    commands. This change make sure we run the discover on every deploy run
+    which is required for scaling up events.