bump default cpus to get better throughput when ohai is wrong

This is going to be a no-op on linuxes, but on solaris and other OSen where we don't have good cpu detection in OHAI (which is admittedly a bug, but not one getting fixed particularly quickly) this will make compiles faster in the 2-[v]cpu case.  Users on single-core solaris boxes might get some increased contention.  Even our ancient v245s have 2 cores though.