(CPR-54) Move deb_repos tasks into Pkg::Deb::Repo

This commit moves the content of the three tasks in deb_repos.rake into
lib/packaging/deb/repo.rb. This allows the rake tasks to be thin
wrappers around method calls and allows the methods to be tested at some
level. It also allows more code reuse in sane ways than parameterised
rake task calls.
(maint) Update rsync_* to use Pkg::Util::Execution.ex
(CPR-54) Move ship_repo_configs into Pkg::Util::Net

Rather than invoke rake tasks from the newly librarified deb repos
methods, it is far cleaner to invoke other ruby methods. This commit
moves the ship_repo_configs task into Pkg::Util::Net so that it can be
easily called from Pkg::Repo::Deb.
(CPR-54) Refacter lib/packaging/deb/repo.rb

This commit makes some minor refactors to Pkg::Deb::Repo for both
correctness and cleanliness. First, all instances of find_tool with an
error are replaced with check_tool, which generates an error
automatically when the tool cannot be found. Second, sh is replaced by
Pkg:Util::Execution.ex to remove the dependency on rake in the library.
Similarly, FileUtils is required and then directly referenced in mkdir_p
calls to avoid the dependency on 00_utils. Finally, repo_urls is now
set outside an if block so that there is no need to initialize it as an
empty array. This also adds a base_url method that returns the builds
url that is shared between repos and repo_configs.
(CPR-54) Add repo_creation_command to Pkg::Deb::Repo

This commit decomposes the deb create_repos method into two smaller
methods. create_repos now calls out to repo_creation_command to generate
the command to create the repo. This will enable both methods to be
tested cleanly.
(CPR-54) Add tests for Pkg::Deb::Repo

This commit adds some basic tests for the Pkg::Deb::Repo module.