Refactor the debian test fixtures building
Ticket moved to GitHub: "pulp/pulp_deb/395":https://github.com/pulp/pulp_deb/issues/395
The idea is to use best Makefile practices.
Currently, we are building all packages multiple times for each repository.
Instead, packages should have there own make targets which are dependent targets of the repositories that need them.
Ideally all built repositories could share a common pool folder (either directly or using symlinks), so we do not build an unnecessarily large fixtures container. This might be prohibitively hard to achieve with the current repo building tooling.