ara_api role: allow retries when attempting to run sql migrations

We've seen sql migrations unexplicably fail in integration tests against
mysql and postgresql only to succeed if ran manually later.

It doesn't hurt to re-try migrations if the command hasn't succeeded the
first time around so implement a retry to see if this improves the
success rate.

Change-Id: Id10bfb9a643bbb3ec1907580826104ded30db2a6

roles/ara_api/tasks/database_engine/django.db.backends.mysql.yaml

@@ -48,3 +48,7 @@
     PATH: "{{ path_with_virtualenv | default('/usr/bin:/usr/local/bin') }}"
   command: ara-manage migrate
   run_once: true
+  register: _ara_sql_migrations
+  retries: 3
+  delay: 5
+  until: _ara_sql_migrations is succeeded

roles/ara_api/tasks/database_engine/django.db.backends.postgresql.yaml

@@ -48,3 +48,7 @@
     PATH: "{{ path_with_virtualenv | default('/usr/bin:/usr/local/bin') }}"
   command: ara-manage migrate
   run_once: true
+  register: _ara_sql_migrations
+  retries: 3
+  delay: 5
+  until: _ara_sql_migrations is succeeded