Updated country population task for ecommerce

We now make use of the management command's initial-only flag silently exit if the countries table is already populated.

ECOM-7422

playbooks/roles/ecommerce/tasks/main.yml

@@ -83,19 +83,12 @@
     - migrate:db
 
 - name: Populate countries
-  shell: "DB_MIGRATION_USER={{ COMMON_MYSQL_MIGRATE_USER }} DB_MIGRATION_PASS={{ COMMON_MYSQL_MIGRATE_PASS }} {{ ecommerce_venv_dir }}/bin/python ./manage.py oscar_populate_countries"
+  shell: "DB_MIGRATION_USER={{ COMMON_MYSQL_MIGRATE_USER }} DB_MIGRATION_PASS={{ COMMON_MYSQL_MIGRATE_PASS }} {{ ecommerce_venv_dir }}/bin/python ./manage.py oscar_populate_countries --initial-only"
   args:
     chdir: "{{ ecommerce_code_dir }}"
   become_user: "{{ ecommerce_user }}"
   environment: "{{ ecommerce_environment }}"
   when: migrate_db is defined and migrate_db|lower == "yes"
-  # the `register` and `failed_when` directives below are here to emulate idempotency for this oscar command.
-  # if and when https://github.com/django-oscar/django-oscar/pull/1841 is merged, the directives can be removed
-  # in favor of the (proposed) --initial-only command option.
-  register: command_result
-  failed_when:
-    - "'You already have countries in your database' not in command_result.stderr"
-    - "command_result.rc != 0"
   tags:
     - migrate
     - migrate:db