Define condition for the first play host one time

We use the same condition, which defines against what host some "service"
tasks should run against, several times. It's hard to keep it the same
across the role and ansible spending additional resources to evaluate
it each time, so it's simpler and better for the maintenance to set
a boolean variable which will say for all tasks, that we want to run
only against signle host, if they should run or not now.

Depends-On: https://review.opendev.org/755484
Change-Id: If7f26c8020d4b02ab9e82dcb69a7ba91a3b5d145

defaults/main.yml

@@ -243,3 +243,6 @@ trove_services:
     execstarts: "{{ trove_bin }}/trove-taskmanager"
     init_config_overrides: "{{ trove_taskmanager_init_config_overrides }}"
     start_order: 3
+
+_trove_is_first_play_host: "{{ (trove_services['trove-api']['group'] in group_names and inventory_hostname == (groups[trove_services['trove-api']['group']] | intersect(ansible_play_hosts)) | first) | bool }}"
+_trove_conductor_is_first_play_host: "{{ (trove_services['trove-conductor']['group'] in group_names and inventory_hostname == (groups[trove_services['trove-conductor']['group']] | intersect(ansible_play_hosts)) | first) | bool }}"

tasks/main.yml

@@ -37,8 +37,7 @@
 
 - import_tasks: db_setup.yml
   when:
-    - "trove_services['trove-api']['group'] in group_names"
-    - "inventory_hostname == ((groups[trove_services['trove-api']['group']]| intersect(ansible_play_hosts)) | list)[0]"
+    - _trove_is_first_play_host
   vars:
     _oslodb_setup_host: "{{ trove_db_setup_host }}"
     _oslodb_ansible_python_interpreter: "{{ trove_db_setup_python_interpreter }}"
@@ -55,8 +54,7 @@
 
 - import_tasks: mq_setup.yml
   when:
-    - "trove_services['trove-api']['group'] in group_names"
-    - "inventory_hostname == ((groups[trove_services['trove-api']['group']]| intersect(ansible_play_hosts)) | list)[0]"
+    - _trove_is_first_play_host
   vars:
     _oslomsg_rpc_setup_host: "{{ trove_oslomsg_rpc_setup_host }}"
     _oslomsg_rpc_userid: "{{ trove_oslomsg_rpc_userid }}"
@@ -169,12 +167,12 @@
       - name: "{{ trove_service_name }}"
         type: "{{ trove_service_type }}"
         description: "{{ trove_service_description }}"
-  when: inventory_hostname == groups['trove_api'][0]
+  when: _trove_is_first_play_host
   tags:
     - trove-install
 
 - import_tasks: trove_db_sync.yml
-  when: inventory_hostname == groups['trove_conductor'][0]
+  when: _trove_conductor_is_first_play_host
   tags:
     - trove-install