OLT left in device list after delete, but not found when attempting to delete

To reproduce:

1. create/enable BBSIM device
2. pass EAPOL
3. enable access in ONOS
4. pass DHCP
5. issue the following command
   1. 
      voltctl device disable $(voltctl device list --orderby Root -q); voltctl device delete $(voltctl device list --orderby Root -q)
   2. It is important that this is a single command line to minimize the time between the disable and delete
   3. this was discovered via robot testing where there is not delay between commands

the delete of the OLT device should fail and a `voltctl device list` should show the OLT as disabled. If you attempt to delete the OLT again it will get a not-found error.

so odd that it is in the device list, but can't be deleted.