N-way benchmarking

Make loadgen-snabb-nic-guest.sh run in parallel multiple loadgen/snabb/qemu instances.
The current updates relies on proper description of the PCI/NUMA node/CPU affinity in /etc/pci_affinity.conf. I have created this file on both chur and grindelwald.

The trick is that CPU column is pointing where to run QEMU. The corresponding snabb is running on CPU+1.
Loadgen will be run as a separate instance for each NUMA node feeding the attached PCI devices.

The changes in the bench_conf.sh include:
RUN_LOADGEN - have to be set for the script to execute loadgen design
NFV_PCI0 - a quoted list of snabb/qemu attached PCI devices
NFV_PCI1 - a quoted list of loadgen design PCI devices