rusty-gd: no more sleep

since it's backed by a fd, a structure that encourages reuse is a good
thing.

integrate this into HCI, for command timeouts

Bug: 171749953
Tag: #gd-refactor
Test: gd/cert/run --rhost SimpleHalTest
Change-Id: I3094c7a666281cebdfdeee05246ac1ad557988c5