[2.1] Add support for migrating logs from 2.0 to 2.1

- some code cleanup and refactors
This is a smell. The stinker in this case is that lucene log migration should be happening from the lucene module. It would appear however that it is not worth going through all the trouble of registering lucene as a log upgrader.  This should be dealt with in the context of a concerted effort to provide a unified upgrade framework.