Add run_once missing from some migrate tasks.

playbooks/roles/edx_django_service/tasks/main.yml

@@ -124,6 +124,7 @@
   environment: "{{ edx_django_service_environment }}"
   with_items: '{{ edx_django_service_post_migrate_commands }}'
   when: migrate_db is defined and migrate_db|lower == "yes" and item.when | bool
+  run_once: yes
   tags:
     - migrate
     - migrate:db

playbooks/roles/edxapp/tasks/service_variant_config.yml

@@ -129,6 +129,7 @@
 - name: migrate
   command: "{{ COMMON_BIN_DIR }}/edxapp-migrate-{{ item }}"
   when: migrate_db is defined and migrate_db|lower == "yes" and COMMON_MYSQL_MIGRATE_PASS and item != "lms-preview"
+  run_once: yes
   environment:
     DB_MIGRATION_USER: "{{ COMMON_MYSQL_MIGRATE_USER }}"
     DB_MIGRATION_PASS: "{{ COMMON_MYSQL_MIGRATE_PASS }}"