Move tarball create task into its own Rake file

Signed-off-by: Moses Mendoza <moses@puppetlabs.com>
Add a Rake file with a task for cloning the packaging repo

Signed-off-by: Moses Mendoza <moses@puppetlabs.com>
Add loading of new separate tasks to top-level Rakefile

Signed-off-by: Moses Mendoza <moses@puppetlabs.com>
Remove all rpm-related tasks and variables from Rakefile

We're going to let the packaging repo handle this.

Signed-off-by: Moses Mendoza <moses@puppetlabs.com>