Support native naming in InstanceGroup

The branch adds support for the native neutron load balancer resource in
in InstanceGroup. It also raises an error if a non load balancer
resource is passed.

Implements: blueprint lbaas-resource
Change-Id: I9b6e7341e2d3c9f14be704c7fbce1e318efbc2d4
Merge "Support native naming in InstanceGroup"