If a node is suspended and receives an unknown or failing audit,
disqualify them if the grace period (default 1w in production) has
passed.
Migrate the nodes table so any node that is currently suspended gets
unsuspended when the satellite starts up.
Change-Id: I7b81c68026f823417faa0bf5e5cb5e67c7156b82
* change overlay.UpdateStats to allow a third audit outcome. Now it can
handle successful, failed, and unknown audits.
* when "unknown audit reputation"
(unknownAuditAlpha/(unknownAuditAlpha+unknownAuditBeta)) falls below the
DQ threshold, put node into suspension.
* when unknown audit reputation goes above the DQ threshold, remove node
from suspension.
* record unknown audits from audit reporter.
* add basic tests around unknown audits and suspension.
Change-Id: I125f06f3af52e8a29ba48dc19361821a9ff1daa1
