Handle exceptions when deleting networks and ports with NVP

- if network/port doesn't exist in NVP anymore, delete from quark db
- if network/port does exist in NVP, delete from quark db and then add
  info about it to new orphaned db tables for clean-up by sysadmins later

RM6485
Looking at definition of `_lport_delete` below, should `switch.nvp_id` be `switch`?