Use Twisted testcase from a separate package

Problem description
===================

We want to open-source the plumbing code for testing Twisted reactor.
To do so, we need to move it in a different package.

chevah.commons code is already public... but it is of low quality and it contains project specific code.

By moving  this code into a separate package it should be much easier to let other use the code.


Changes description
===================

chevah-rhinoplasty package was created with code from here: https://github.com/chevah/chevah-rhinoplasty

There is also a merge code from server, but a small change. But this needs to go after 986 was merged as it is based on 986.
https://github.com/chevah/server/pull/51


How to try and test the changes
===============================

Run paver deps, and then paver test.