Send delete.end with latest instance state

Delete.end notifications were getting sent with a blank deleted_at
field. This meant that services listening to notifications for
instance state changes could potentially never get the instances
deleted_at value. The instance usage audit notification would be
the only source for that value.

This change returns the destroyed instance from the conductor API
and sends the delete.end notification with that state, containing
the deleted_at value which was just set.

UpgradeImpact
Closes-Bug: #1241681
Change-Id: I3481e0bada1711c3bff50f249f6a2b40a4ea6855