Add Ubuntu 12.04 support

ubuntu-setting has common code for ubuntu 10.04/12.04
The different between 10.04/12.04 is DHCP server
10.04 : dhcp3-server
12.04 : isc-dhcp-server

Signed-off-by: Kuninori Morimoto <kuninori.morimoto.gx@renesas.com>