Adjusted build_mesos to build 0.20 style python debs

Closes #7 

With this patch I make the new save_python_eggs build debs that are compatible with the new way that mesos python packages are namespaced (mesos.native, mesos.interface)

I'm also building them in a *different* way, using the local files and the setup.py instead of the postinstall egg method. I think this is a good thing and makes the debs more "normal".

Because of the way fpm needs the package names and stuff, I do some special string manipulation to get the right version and package names, determined by the egg given. (should be sustainable as mesos makes more python submodules)