Fixed method rewriting in Ruby client

[mfojtik]

Hi,

There is a weird issue with Realms in Ruby client code, you can try it
using the Mock driver:

api.realms[0].name  => "Europe"
api.realms[1].name  => "Europe" / "United States" is expected value here

(api is instance of DeltaCloud::API)

So I replaced 'static method generation' with 'attr_accestor' and
then setting attribute value explicitly.

This works both in Rails and RSpec.

 -- Michal