Changes to remove the use of mapping tables from Nuage plugin

Nuage plugin maintains a mapping of Openstack and Nuage resources.
With this change Nuage VSD can itself maintain this mapping, so the
plugin doesn't have to store the information in the neutron DB.
This eliminates potential out of sync and upgrade issues.

Closes-Bug: #1338853

Change-Id: I03b32a83d792c742962e0195383a622c1967ae4f
Merge "Changes to remove the use of mapping tables from Nuage plugin"