Havana removed passing in the conductor_api to get_instance_nw_info

Fixes OS-234

The interface changed to network_api.get_instance_nw_info(...) to
no longer take the conductor_api. This was used before because
the network_api method may access the database directly. Now the
method always makes an RPC call to the network manager to get this
information.

Change-Id: I417854d8893f0d5dae130ff99d9b0482eb040583