control: use number of pools instead of modules for shutdown delay
control: use number of pools instead of modules for shutdown delay

By using the number of existing pools instead of the number of modules
we minimize the time needed for all modules to finish processing.
Since all modules (internally) belong to one pool, continuing for
<#pools> more rounds, each module will receive all input by other
modules of all rounds and therefore have a chance to process itself
before shutdown.

nilsonholger/bvs,nilsonholger/bvs,nilsonholger/bvs,nilsonholger/bvs