Use Packetary for downloading MOS rpm/deb packages

Currently we use yumdownloader/debmirror for downloading packages from rpm/deb repos while building ISO. To mix packages from different repos we use EXTRA_*_REPOS variable. Due to some limitations of these native tools our current build code is quite messy. The best way to define a set of repos is to use the same data structure like we have in fuel-menu or fuel-web. It is a flat prioritized set of repos. Packetary allows to download packages from many repos using this flat data structure. We are planning to use packetary both in our infrastructure (as a part of build process) and on the user side (as a part of creating local repos).