Improve nova-ironic cellv2 discovery

Use the existing nova-compute cellv2 discovery logic for nova-ironic too, now
that we have the --by-service flag.
The nova_api_discover_hosts.sh script will now wait (up to 10 minutes) for all
nova-compute and nova-ironic services to register, then run host discovery
with --by-service to create host mappings for all services. We no longer need
ironic nodes to be deployed on the nova-ironic services for discovery to work.
We also no longer need to enable the priodic job.

Related nova change Ie9f064cb9caf6dcba2414acb24d12b825df45fab

Related-Bug: #1755602
Change-Id: I723237ae7285f3babd6eceb1ce7da4e2734d1e4f

docker/services/nova-api.yaml

@@ -185,7 +185,8 @@ outputs:
               fi
             done
             echo "(cellv2) Running host discovery..."
-            su nova -s /bin/bash -c "/usr/bin/nova-manage cell_v2 discover_hosts --verbose"
+            su nova -s /bin/bash -c "/usr/bin/nova-manage cell_v2 discover_hosts --by-service --verbose"
+
         nova_api_ensure_default_cell.sh:
           mode: "0700"
           content: |

docker/services/nova-ironic.yaml

@@ -60,6 +60,7 @@ outputs:
     description: Role data for the Nova Compute service.
     value:
       service_name: {get_attr: [NovaIronicBase, role_data, service_name]}
+      cellv2_discovery: true
       config_settings: {get_attr: [NovaIronicBase, role_data, config_settings]}
       logging_source: {get_attr: [NovaIronicBase, role_data, logging_source]}
       logging_groups: {get_attr: [NovaIronicBase, role_data, logging_groups]}

environments/services/ironic.yaml

@@ -4,5 +4,3 @@ resource_registry:
   OS::TripleO::Services::IronicPxe: ../../docker/services/ironic-pxe.yaml
   OS::TripleO::Services::NovaIronic: ../../docker/services/nova-ironic.yaml
   OS::TripleO::Services::IronicNeutronAgent: ../../docker/services/ironic-neutron-agent.yaml
-parameter_defaults:
-  NovaSchedulerDiscoverHostsInCellsInterval: 15