- Defaults to `1.1.1.1`
- Add more Ping integration tests with different addresses
- Add unit test pinging 127.0.0.1
- Add comment explaining why we need to use ICMP instead of UDP
- `HEALTH_OPENVPN_DURATION_INITIAL` renamed to `HEALTH_VPN_DURATION_INITIAL` with retro-compatiblity
- `HEALTH_OPENVPN_DURATION_ADDITION` renamed to `HEALTH_VPN_DURATION_ADDITION` with retro-compatiblity