Use latest Ubuntu 16.04 LTS guest image.

The release we are using is more than a year old, let's update to a
recent release in order to make sure we stay up to date.

Change-Id: Ie0f5266707483a69ea8d6d4f63ca39f26552fc24
Co-Authored-By: Luong Anh Tuan <tuanla@vn.fujitsu.com>
1 file changed