Ironic discoverd database is not cleared out when ironic nodes are deleted

Issue

• When deleting ironic nodes and reregistering/rediscovering, old data may be left in the discoverd database which prevents discovery.
• Ironic nodes seem to be stuck introspecting.

[stack@dhcp-75-176 ~]$ openstack baremetal introspection bulk start
Preparing for deployment...
  Discovering nodes.
    Sending node ID f3af18c3-e289-4d87-8002-9c3d5cff47fc to discoverd for discovery ... ERROR:  openstack Some or all of bmc_address's ['10.34.74.221'] are already on introspection.