Don't unlock the task if lock_expiry is still valid

[aguedob]

Hi!

In my use case I need the task result to be cached until the lock time expires, in order to avoid new tasks with the same input data.
Does it make sense to you keeping the lock even if the task has finished?

[steinitzu]

I would rather add a new parameter for this so it's not such a dramatic change in behaviour. E.g. unlock_when_finished (default True)

[steinitzu]

Possibly even separate params: unlock_on_success / unlock_on_failure