Add attributes schema to OS::Neutron::FloatingIP

FloatingIP now validates attributes against a schema instead of
accepting all possible inputs and filtering on the result returned by
neutron.

Change-Id: I3bf1c3728a9d6faab71c2312f331d73b1460c013
Closes-Bug: #1240893
Merge "Add attributes schema to OS::Neutron::FloatingIP"