[Schema] Clean VMI and instance IP correctly

The VirtualMachineInterfaceST object list is not clean properly and
growing with time.

- Add function to catch the VMI delete event.
- If schema fails to read VMI or IIP on the API, delete IIP or
VirtualMachineInterfaceST into the list.
- And that patch also exit the 'process_pool_result' method if none of the
poll requests call a schema method.

Closes-bug: #1382397
(cherry picked from commit 75458b4509f50f49c99c54ba3f61c5c86bb89ef2)
Change-Id: Ib386ea5b53fbaea4ae15b34c1c74837b06b258ef