Rbarlow package distributed tasks

This (large) pull request:

* Packages Celery 3.1 and all of its dependencies so that we can carry it in our repository
* Adds init.d scripts for Pulp's various Celery workers under Upstart systems
* Adds unit files and related helper scripts for Pulp's various Celery workers under systemd systems
* Unit tests for the "related helper scripts"
* Adds support for these init scripts and systemd units to our pulp-dev script

This pull request does not contain any changes to documentation. It's big enough as it is, so I will be submitting a separate pull request for that.