Adds a configurable work around for the sector imbalance problem.
the selectorIndexPerHostMap is now a hashmap and created lazily + added some serve warning when feature enabled
Resolved some checkstyle issues
Merge pull request #4044 from pveentjer/fix/3.x/connection-imbalance

A workaround to prevent selector imbalance
It has to be removed once #4045 is fixed.