HBI emits messages for create/update/delete of host data.  Swatch-metrics-hbi currently implements logic to translate create/update HBI events into swatch events and tracks HBI host relationships as events are processed, but does not delete them yet.

This card is to translate HBI delete events into a Swatch INSTANCE_DELETED event and to update the relationships accordingly.

Acceptance Criteria

• If swatch-metrics-hbi encounters an HBI event for DELETE and a relationship exists for the target host:
      - The existing relationship is deleted
      - A Swatch event is sent containing:
          - Last known metadata about the host (display name, inventory_id, ...)
          - Last known calculated measurements
          - Timestamp of the incoming delete event, truncated to the hour of the event.
      - If the target host is a hypervisor, for each affected guest:
          - Update the guest relationship to reflect that it is now un-mapped.
          - Re-normalize the guest's facts based to reflect that its hypervisor was deleted and send an INSTANCE_UPDATED event with changed metadata/metrics.
      - If the target host is a guest and is mapped:
          - No other relationship updates required.
          - If the mapped hypervisor relationship exists, re-normalize the facts for the hypervisor and send an INSTANCE_UPDATED swatch event for the hypervisor.
• If no relationship exists for the host that was deleted:
      - send a bare swatch INSTANCE_DELTED event with any host data that was included in the incoming HBI delete event.
      - Log a WARNING
• If the unleash flag is enabled, no swatch events should be emitted.  Emitting the swatch delete event is out of scope to this card.