Comment 0 for bug 1464806

L3 plugin code (neutorn/db/l3_*_db.py) calls l2 plugin with tenant_id=''(empty string) for creation port and subnet for internal use.
e.g. gateway port, floating ip port, port used by dvr.

This is ugly hack and some L2 plugin or ML2 mechanism driver doesn't expect it and be confused with it.
It is better to fix it.

tenant_id=''(empty string) is used for those purpose.
- prevent (non-admin) user from updating
  NeutronDbPluginV2._enforce_device_owner_not_router_intf_or_device_id
- prevent (non-admin) user from deleting
 NeutronDbPluginV2 ._delete_port
- don't count for quota
  Controller.create

This dirty hack was firstly introduced by
the changeset of a7326a947bc0b30778e06acd772dd38bcb28d96d
the change id of Ice72fc6d3b1c613d596c037818ed66d7e9ed841d
with only one line comment. The followers just use it without any