don't import events for inactive hosts

[Gudule Lapointe]

Don't import events from hosts that have failed for more than one day.

• if unknown host (never registered), do import
• if host was registered, but is deregistered (without failure), do import
• if host was registered, but is deregistered after too many failures, don't import

Shorten the time before marking deregister to maximum 1 day (currently around 1 week)

Edited: hosts could be unregistered or (deregistered) for a number of reasons, it doesn't mean they are not active, so we should not take the registration status in account, only the check fails.