Floatingip extension support for nuage plugin

Nuage's VSP supports adding floating-ip which fits
nicely with this floatingip extension supported by
openstack's neutron. This set of change enables that.

Implements: blueprint floatingip-ext-for-nuage-plugin

Change-Id: I7178ef0dd170567d0e50035eeed0db2ca33f6c1a
Merge "Floatingip extension support for nuage plugin"