Support for multiple DNS server IP addresses

[jdsnape]

At the moment ocproxy just takes the first IP address it is given and ignores any others.

We had an issue recently where the first DNS server was not working, and anyone using ocproxy couldn’t use the VPN until it was fixed, whereas people using open connect ‘natively’ failed over to the second server.

I know DNS servers can be specified manually, but it would be good if ocproxy could fallback to the other servers provided.