Add support for reading 2.1 log files
Such a feature is needed to upgrade from 2.1 to 2.2 when using HA
Add a test case for upgrading from 2.1 to 2.2 in all scenarios: embedded, server, and HA
Various cleanups and small improvements
Add support for upgrading from 2.1 store

- bumped store version for 2.2 to 0.A.4
- introduce tests for upgrading from each older version: 1.9, 2.0, and 2.1
- cleanups and improvements
Merge pull request #2893 from davidegrohmann/2.2-read-2.1-logs

Support for reading 2.1 log files and upgrading from 2.1 store files