Fix various breakage in restbase-cassandra

Our tests are evidently not very good yet; we really need to start testing
stopping & restarting a restbase server.

Changes in detail:
- Version meta tables for consistency with all other tables. Use
  makeSchemaInfo to make sure all expected schema metadata is generated.
- Fix a broken call to _get that didn't pass the table in
- Add some primitive error debug prints; really need to convert this into real
  logging.
Release restbase-cassandra v0.2.7
Only use a batch when needed for consistency

Bug: https://phabricator.wikimedia.org/T76688
Unconditionally create tables

We are using IF NOT EXISTS already, so table creation is idempotent. Schema
migration etc needs to be handled in the _createTable handler.
Merge pull request #25 from gwicke/master

Fix various breakage in restbase-cassandra