Implements #3669
Implements #3669

Adds indices around ports, networks and subnets to improve performance
around oft-made calls to Neutron, such as get_instance_nw_info.

lmaycotte/quark,lmaycotte/quark,insequent/quark,asadoughi/quark,Cerberus98/quark,alanquillin/quark,Cerberus98/quark,alanquillin/quark,rackerlabs/quark,roaet/quark,rackerlabs/quark,roaet/quark,insequent/quark,asadoughi/quark,blamarvt/quark