Rafactor glance api to merge defaults

This code cleanup simplifies one the tests by merging the
specified params over the defaults instead of returning either
the defaults or the specified params.

spec/classes/glance_api_spec.rb

@@ -41,8 +41,9 @@ describe 'glance::api' do
   ].each do |param_set|
 
     describe "when #{param_set == {} ? "using default" : "specifying"} class parameters" do
+
       let :param_hash do
-        param_set == {} ? default_params : params
+        default_params.merge(param_set)
       end
 
       let :params do