Spec test for domain template to verify rendering

Add basic spec tests for the domain template to test rendering through
simple wrapping of a config object to provide values for class instance
variables used by the template as it mostly mirrors those required.

spec/support/libvirt_context.rb

@@ -24,5 +24,7 @@ shared_context "libvirt" do
 
     # return some information for domain when needed
     allow(domain).to receive(:mac).and_return("9C:D5:53:F1:5A:E7")
+
+    machine.stub(:id => id)
   end
 end