Add some unit test plumbing

* Add a base test class derived from oslotest
* Remove py33 support from tox
* Cleanup pep8 errors

Change-Id: I05da4d1c6627e055d522772e43aa962184165291
Add publisher infrastructure

Adds plumbing for "publishers."  Publishers are strategy classes
responsible for preparing images for distribution.

An example publisher should be a BitTorrent publisher that took the
image binary, generated a torrent file from it, and started an initial
seeder process.

The default publisher is NopPublisher, which takes no action.

Change-Id: I8fd952270aaf4fc6962dafc1f287aca0cd0c9828