add DNS testing to Windows automatic build/test client infra

[cron2]

copying from IRC so it's not lost

17:25 <@cron2> lev__: you might actually be able to test that on the windows 
               build thingie
17:26 <@cron2> if you do "--setenv UV_WANT_DNS dns --push-peer-info" the 
               reference server will push "--dns" to you, and with "UV_WANT_DNS 
               dhcp" it will push "dhcp-option DNS"
17:27 <@cron2> 10.194.x.x stuff, so it needs to be in proper byte order
17:27 <@cron2> and then you do ping tests on ping4.open.vpn/ping6.open.vpn, 
               which is only resolvable on this nameserver
17:27 <@cron2> not sure if your rig can do ping on DNS names
17:27 <@cron2> works nicely in unix t_client