Faster starts, pauses and stops

A new sandbox runs its first command 331 ms after the create request at the median, down from 374 ms, and 30 of 40 creates were running in under 200 ms. A pause answers in 165 ms, down from 226 ms, and a snapshot is ready in 3.27 s. On the server, without the network to Virginia, a pause answers in 81 ms, a wake in 75 ms and a stop in 37 ms; the speed page now shows those figures beside the ones from a laptop.