Upgrade Jenkins jobs to use Python scripts for pre and post upgrade tasks

[omaciel]

Since we will be replacing some bash scripts for Python scripts for pre and post upgrade tasks, let's also update our existing Jenkins jobs to use the new scripts.

These scripts will be managed within Pulp Smash.

Please see #517 and #519 for more info.

[kdelee]

@kersommoura

All of tools that I was working for this are in https://github.com/PulpQE/pulp-migrate but some more expansion of the content types and repo types (sync, lazy sync, upload, etc) should probably happen.

The tests in pulp-smash currently test for existence, sync-ability, and do some downloading of published content. This is already an improvement on the post-upgrade.sh tests (see below) which only test for existence.

The scrips currently used by the upgrade jobs are still these ones:
https://github.com/pulp/pulp_packaging/blob/master/ci/jjb/scripts/pre-upgrade.sh
https://github.com/pulp/pulp_packaging/blob/master/ci/jjb/scripts/post-upgrade.sh