We broke 'apt_sources_list' and 'apt_preferences' options quite a while
ago. Turned out that fix is quite simple.
This change adds empty sources.list and apt-preferences files which are
always added into images. If kolla-build.conf will use any of APT
related options then those files will be replaced with provided ones.
Ubuntu is a bit different than centos. We aren't pinning a single ceph
verion because we cannot. We can however pin to a particular repo,
but we were not due to formating. This fixes that formating and pins
to a specific repo.