Configurable forwarding and cpus

A take on making whether to forward ports as well as the number of cpus configurable.

Two things that should be considered:
1. The forwarding-configuration might be a bit to fine-grained, in my case I just wanted everything switched off, it could be enough just to have one configuration for whether to do the forwarding at all
2. I have only tested the cpu-configuration on virtualbox, no idea whether the same configuration works on vmware