br: log advancer for testing retires owner but etcd session still alive

## Enhancement
Right now using retire doesn't actually delete key from etcd. should close the etcd session as well to mimic the instance down so can trigger election

Start by locating the testing log advancer's retire operation and the code that manages its etcd session. Trace how retirement currently affects the owner key and how elections are triggered. Done means retiring the owner also closes the etcd session, removes the key, and allows the election behavior to be tested.

Written by the indexing model from the issue text.