Move Zake driver code to separated Python module

That is needed to prevent Zake driver load in real-life Zookeeper
usage - currently we had the situation when even if you want to use
just KaZoo, you needed to install partially test-requierements
(zake package).

Change-Id: I9664fda2d6e76a6e48776b4a6d92af4c4baf1425
Merge "Move Zake driver code to separated Python module"