Drop same-code Python2 support

[Jason Gerard DeRose]

Python2-support was added to Microfiber basically just to make migrating our components to Python3 easier.

But now everything has migrated to Python3 except for `dc3`. The hold up with `dc3` is you can't currently create DBus servers using PyGI, so we're stuck using the static Python2-only python-dbus bindings.

However, there is no reason dc3 can't keep using Microfiber 11.09. Heck, I'm not against copying and pasting a Python2-friendly version of Microfiber into dc3 as a stop-gap. Whatever. Velocity and quality over purity.

Right now we support Python 2 & 3 in the same code (made unit testing easier, plus saved me having to figure out 3to2). But as Microfiber is such a critical piece of code that nearly our entire component stack depends upon, it needs to be simple and clear and to have an unholy boatload of unit tests. So I want to drop the Python2 cruft ASAP.

Assuming 3to2 works okay on Microfiber, we might as well still produce a Python2 package as it means more potential Microfiber users, more good PR for Novacut. But if it's a hassle and we encounter problems, Microfiber 11.09 will be the last with Python2 support. 11.09 is still a very high quality release, so it's not like we're leaving them out in the cold.

But seriously, everyone needs to come bask in the warm Python3 glow!

I'm really burning to do this, so sorry community, I'm not sharing this one :P