Add support for pb_numbers rake task

Related: https://github.com/mdsol/kender/pull/48

**Background**
Chad, created the ```pb_numbers``` gem that provides a ```pb_numbers:list:duplicates``` rake task that verifies all pb numbers in your test suite are unique. This PR updates ```kender``` to run that task if available as part of the ```ci:run```.

I have a PR open to the ```pb_numbers``` gem so it return status of 1 if duplicates are found which allows kender to know if a test has succeeded or not. https://github.com/mdsol/pb_numbers/pull/1. I prefer to wait for that PR to get merged before this is merged.

Tested locally and all works as expected. Thanks!

@jcarres-mdsol  @mjobin-mdsol @asmith-mdsol Please review & merge when satisfied