(maint) Migrate ex to Pkg::Util::Execution

This commit migrates ex from 00_utils to a new module called
Pkg::Util::Execution. It also adds another method called success?, which
wraps the behavior of $?.success?, with the bonus of being more easily
stubbed/mocked in other tests. Some basic tests are included for ex. The
implementation of ex is moved from %x to `` to enable testability of the
method.
(maint) Update Pkg::Util::File for new Pkg::Util::Execution
(maint) Update 00_utils for Pkg::Util::Execution
(maint) Update Pkg::Util::File.mktemp to use Pkg::Util::Execution.ex instead of ``
(maint) Address order dependent test failures in Pkg::Util::Net

Because the net spec tests around ssh stub out ssh calls, there is no
guarantee that the $? object will be instantiated, which can cause tests
to fail if we try to get success? from nil. This commit updates the
tests to use the Pkg::Util::Execution.success? method, which is easily
stubbed out in tests. The implementation is also updates to use the same
method.
Merge pull request #315 from haus/maint/master/add_pkg_util_execution

(maint) Migrate ex to Pkg::Util::Execution
(RE-1822) 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.
(maint) 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.
(maint) 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.
tests
refactoring
More fileutils additions
more refactoring of deb repos
tests that work
Add repo_creation_command to decompose deb create_repos into smaller methods
more tests