Don't install VPN if PSK/Username/Password is not changed by user

[VarunAgw]

I recently re-installed it on an old server. I forgot to change username/password and just ran the script absentmindedly, hoping it will not change the old username/password. I couldn't test it earlier and today I found my server was open to anyone for last 2 days

So my suggestion is to require change in username/password before allowing anyone to run it or best just ask all these details at runtime using read function .