add DNS support for ubuntu12.04 server

I used static ip in my ubuntu12.04 server, but I can't not access the internet,
I can't ping through www.bing.com.

add `dns-nameservers' to /etc/network/interfaces, like code below:

auto eth0
iface eth0 inet static
address 192.168.1.2
gateway 192.168.1.1
network 192.168.1.0
dns-nameservers 8.8.8.8 8.8.4.4
              

Note the "s" at the end of "nameservers". You need to use "nameservers" even
if you have only one.