Simplify worker_loop
Fix run_games exception

Currently after the first exception we send api/failed_task
to host that set the task as not active. So when we retry (up
to five times) and in case succed, when we send updated_task
result is ignored because task is not active anymore.

So fix it allowing the worker to retry forever but redo the
full loop, starting from getting a new task.
Retry forever also request_task

At this point makes sense to extend the retry-forever
logic also to request_task.
Add recover option to cutechess
Merge remote-tracking branch 'origin/master'
Merge remote-tracking branch 'origin/master' into userdb
More work moving to userdb