* Systemd service currently marks the mount as read-only, and this is
regarded as good practice for server/daemon only operation.
* Don't create /etc/openvpn/ccd as the mount may be read-only.
* Append the client-config-dir command line argument if it is found to
avoid mkdir operation.
* Mount can easily be modified using a different docker run line with
":ro" on the volume mount.