Setup AFS mirrors for ubuntu-xenial-arm64
Setup AFS mirrors for ubuntu-xenial-arm64

Stop using upstream http://ports.ubuntu.com/ubuntu-ports and switch to
our AFS mirrors. This should help with download speads, since local
mirror, and avoid the issue of building newer images then our mirrors
have packages for.

Change-Id: I083dccdc23eb1586c138ffd138a0afa4e8d2a6f9
Signed-off-by: Paul Belanger <e7139c8e6c4ea75cc1c287ce081b2dc0f3ab39ec@redhat.com>

openstack-infra/project-config,openstack-infra/project-config