Openstack 16.2 to 17.1 - Undercloud system upgrade hangs when net_config_override is present (DB sync)

Issue

• When operator uses the variable net_config_override in undercloud.conf, then Undercloud system upgrade from 16.2 to 17.1 hangs if TLS is configured.

• The following error is logged by Ansible when upgrading undercloud with custom network_config from RHOSP 16.2 to RHOSP 17.1

  TASK | Create containers managed by Podman for /var/lib/tripleo-config/container-startup-config/step_3
  ...
  ERROR: Can't run container neutron_db_sync
  oslo_db.exception.DBConnectionError: (pymysql.err.OperationalError) (2003, "Can't connect to MySQL server on '10.128.8.168' ([Errno 113] No route to host)")