(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.
(CPR-54) Move ship_repo_configs into Pkg::{Rpm,Deb}::Repo

Rather than invoke rake tasks from the newly librarified deb repos
methods, it is far cleaner to invoke other ruby methods. This commit
breaks up the ship_repo_configs task into a Deb and Rpm version and adds
it to the Deb and Rpm repos modules. The ship.rake task is also updated
to invoke both methods.