During sync process only network segments that are bound to a port should be
sent to CVX when creating instances. For that reason, the PortBindingLevel
table should be used to get list of segments bind to a given port.
We can infer the set of tenants to provision from the neutron
networks and ports tables. This is part of a larger effort to
remove any use of arista specific tables and instead make use
of the same data stored in other neutron tables.