Make floating IPs work in private clouds

Private clouds won't have a 'public' network. Due to quirks in Nova as of Folsom, floating IPs are always listed as being associated with the fixed address.  For a public cloud, this network is generally called 'public'. For private clouds it probably isn't.

Really this issue is downstream of both Nova and Fog, but this is a reasonable work around until Nova provides a better way to identify floating IPs.