Implement multiversion/refreshWikiversionsCDB in python

Adds a pure python version of the multiversion/refreshWikiversionsCDB
PHP script.

* Add wmf_realm and datacenter configuration settings
* Add a python implementation of MWRealm's getRealmSpecificFilename
* Import cdblib.py from https://python-pure-cdb.googlecode.com/
* Add tasks.compile_wikiversions_cdb as a refreshWikiversionsCDB
  workalike
* Change tasks.scap to use compile_wikiversions_cdb instead of shelling
  out to PHP script

Change-Id: Ie50be09e724b276a009037a4ee2fd059d1fd87dc