Since VPP binaries are being compiled on host system,
it makes sense to autodetect Ubuntu version when building test images
so that containers would be running version equal to host system.
Type: test
Signed-off-by: Maros Ondrejicka <maros.ondrejicka@pantheon.tech>
Change-Id: I0e13d9ba1ddcd3ad5835bce1b8cccfc048e5e528