Connect to the service only when remote census endpoint is defined

Also return an invalid response when the endpoint is not defined.

This will allow to test remote web services on development environments.

spec/lib/remote_census_api_spec.rb

@@ -90,5 +90,13 @@ describe RemoteCensusApi do
         api.call("1", "12345678Z", Date.parse("31/12/1980"), "28013")
       end
     end
+
+    it "returns an invalid response when endpoint is not defined" do
+      allow_any_instance_of(RemoteCensusApi).to receive(:end_point_defined?).and_return(false)
+
+      response = api.call("1", "12345678Z", Date.parse("01/01/1983"), "28013")
+
+      expect(response).not_to be_valid
+    end
   end
 end