host: Rename parameter in test launching to match data format change.

Signed-off-by: Eric Myhre <eric@flynn.io>
host: During host backend revivification, dispatch container connection attempts in bulk, and gather them later.  This prevents their timeouts from occurring serially, which could cause host service launch to time out in the case of many dead containers.

Signed-off-by: Eric Myhre <eric@flynn.io>