Implement NetBSD-specific subclass of Hardware in the setup module.

Defines memory and CPU facts:
- memfree_mb
- memtotal_mb
- swapfree_mb
- swaptotal_mb
- processor (a list)
- processor_cores
- processor_count
- devices

As a matter of fact, on NetBSD, it is possible to get memory, swap and
processor facts exactly as on Linux. Tested on NetBSD-5, NetBSD-6 and
NetBSD-6.1 (without Linux emulation).