Close the database connections even if exceptions occurred.
Increase database connection limits again.

Worst case we get max 50 connections per process, with currently 16 processes
running == 800 connections and our RDS instance able to handle ~1200.
Remove duplicated db event listener declaration.

There's already a decorator doing the same.
Clean last database result from connections on pool checkin.

Shamelessy stolen from https://github.com/mozilla-services/server-syncstorage/blob/30afe77afd9947b268f91b9f3a9c7bd9540c3df1/syncstorage/storage/sql/dbconnect.py#L329
Let Redis max_connections match DB connection limits.
Remove `error-logfile` from dev run_server command.

The gunicorn_config already lets this default to stdout.
Switch gunicorn to use a gevent-based worker.