(CPR-56) Migrate rpm repo tasks into Pkg::Rpm::Repo

This commit moves the current tasks in tasks/rpm_repos.rake into the
Pkg::Rpm::Repo module. The old tasks now simply forward the request on
to the equivalent method call. This commit also includes a minimum of
refactoring.
(CPR-52) Add nightly_repos rake tasks

This commit is the first incantation of a task set to sign and ship
nightly repos. The main task nightly_repos, handles getting the repos
signed remotely, and then also ships and generates repo configs. As
many of the tasks as possible are ruby calls instead of rake task
invocations.
(maint) Improve deb repo config tests

This commit applies an improvement to the generate repo configs method
in the deb repo module, similar to the rpm tests. It includes some
garbage in the wget results that should be filtered in the process of
generating the repo configs.