Test consumer group reconnect scenario

[agis]

We should emulate an application's deploy procedure (ie. consuming clients of a cgroup disconnect and reconnect eventually) and assert that:

• no messages are lost
• the re-processed messages (if any) percentage stays below a certain threshold

[agis]

Closed by https://github.com/skroutz/rafka/commit/92a76b48bf8221a750def223b6410564bc425928