build: Add local Ubuntu mirror to target image

build: Add local Ubuntu mirror to target image

When deploying via Jenkins CI, the repos used for target image
building are overridden to use the local Ubuntu mirror on Fuel
Master instead of fetching packages from internet.

However, when deploying manually, only bootstrap image building
benefits from the local Ubuntu mirror.

While keeping the internet mirrors, add the local Ubuntu mirror
to target image build repo list.

The first commit (bcdc1eaa74d5efd5f8c80600fb30d722bae9a421) confused
the URL of the local Ubuntu mirror with the local MOS mirror, so I
also cherry-picked a fixup on top.

JIRA: ARMBAND-35

Change-Id: Ibd58067703ce6370781a6b54fd01ce52e29686ac
Signed-off-by: Alexandru Avadanii <Alexandru.Avadanii@enea.com>
(cherry picked from commit bcdc1eaa74d5efd5f8c80600fb30d722bae9a421)
(cherry picked from commit 489b1cb8de7d47c818475f8830e3ea689365e2b3)