Rewrite ipdevpoll's multiprocess mode to use generic worker model

[Morten Brekkevold]

Inspired by Apache's worker model. The multiprocess mode should spawn a number of slave processes that are assigned collector jobs by a master scheduler. The model should even allow for remote worker processes, for distributed collection.

How to launch remote worker processes is out of scope for this task, but should be considered when designing the communication between the scheduler process and the workers.