(RE-3597) Use packaging rake tasks from ruby

The following commits allow the packaging rake tasks to be used from within ruby. This will be useful for shipping projects that don't use the packaging repo fully, but lay down packages in the layout that the packaging repo expects. With this PR, the following can be used to ship via ruby:

```
ENV["PROJECT_ROOT"]="./"
require 'packaging'
Pkg::Util::RakeUtils.load_packaging_tasks
Pkg::Util::RakeUtils.invoke_task('pl:jenkins:ship')
```
Shoudl 't' be 'task' here?