Use domain double instead of machine

spec/support/libvirt_context.rb

@@ -5,14 +5,15 @@ shared_context "libvirt" do
 
   let(:libvirt_context) { true                      }
   let(:id)              { "dummy-vagrant_dummy"     }
-  let(:connection)      { double("::Fog::Compute")  }
+  let(:connection)      { double("connection")  }
+  let(:domain)          { double("domain") }
 
   def connection_result(options={})
     result = options.fetch(:result, nil)
     double("connection_result" => result)
   end
 
-  before do
+  before (:each) do
     # we don't want unit tests to ever run commands on the system; so we wire
     # in a double to ensure any unexpected messages raise exceptions
     stub_const("::Fog::Compute", connection)