openvpn: enable openvpn_persist test for rhel9
The cleanup step for removing openvpn connection is unnecesary and in RHEL9 it might be buggy as we did a connection reload right before it.
This is not a NetworkManager issue, the assert happens when openvpn takes too much to recover and regenerate tun1 interface. Probably NetworkManager could be improved but it seems a corner case that users won't hit.