HostRebootMixin's reboot_host over the command channel: reboot detached
and two seconds late, so the answer comes back before the session goes
down, and a refusal is raised instead of being mistaken for the dropped
session. netOrk sent /sbin/reboot through the private _send_command and
could not tell the two apart (netOrk #1113). A login other than root is
refused before anything runs.
Christian Manivong