plugin/nec: Make sure resources on OFC is globally unique.

V3 and V4 of NEC ProgrammableFlow controller (PFC) generates a network ID
unique inside a tenant. On the other hand, ID mapping table in NEC plugin
expects ID on OFC is globally unique. As a result creation of a network
will fail. To fix it, quantum network ID is passed as ID on OFC.
The same issue happens in port creation too.

In Grizzly this bug was fixed in another way (to support shared network),
but this change is quite big and it cannot be backported.
The minimum way to fix this bug is to specify OFC network ID from Quantum.

Since V3 of PFC does not return network/port ID in the response when ID is
passed in the request, create_network/port is changed to return an ID
passed to the controller instead of extracting ID from the response.

Fixes bug #1127664

Change-Id: Iad1961ee2469b547598e87e63a4a3dc4ac9c6e97