Comment 2 for bug 1302206

The installed should implement one of the suggested solutions on http://askubuntu.com/questions/464507/ubuntu-14-04-server-wifi-wpa2-personal, for example, in /etc/network/interfaces put something like:

auto wlan0
iface wlan0 inet dhcp
wpa-ssid <your_router>
wpa-psk <your_wpa_key>