Namespace deletion can be stuck if not all the ports belonging
to the associated namespace networks are deleted.

This patch enforce proper clean up of subports by:
- Ensuring no request/release VIF actions are processed until the pools
  are recovered by the controller
- Ensure if there are subports leftover when removing a namespace those
  are detached from the pool and deleted regardless of their status

Change-Id: I2cb1586fa1f88bab191af0ead22a2b8afca91a3b

Neutron clears device_owner when port is detached. This means that with
pools we need to consider ports without device_owner set when doing
cleanup on namespace deletion.

Change-Id: Ic38015cba27d8418175027ec4e433df32eae4706