Make dhclient config in ubuntu_network snippet to resemble centos ks' on...

Strongly depens on 
- https://review.openstack.org/#/c/52165/ to fuel-web
- https://github.com/rustyrobot/fuel/commit/e71e01f74ed74f19f1195db32e15c1010e4a3c8e to fuel

Fixes: #PRD-2300

Signed-off-by: Bogdan Dobrelya <bogdando@mail.ru>