get_node_info: Avoid parsing XML in a loop

This refactors the method so it only parses the XML once instead of 4
times. It adds basic tests to avoid regressions.

lib/fog/libvirt/requests/compute/get_node_info.rb

@@ -12,19 +12,25 @@ def get_node_info
             node_hash[param] = client.send(param) rescue nil
           end
           node_hash[:uri] = client.uri
-          xml = client.sys_info rescue nil
-          [:uuid, :manufacturer, :product, :serial].each do |attr|
-            node_hash[attr] = node_attr(attr, xml) rescue nil
-          end if xml
+          if (xml = sys_info)
+            [:uuid, :manufacturer, :product, :serial].each do |attr|
+              element = xml / "sysinfo/system/entry[@name=#{attr}]"
+              node_hash[attr] = element&.text&.strip
+            end
+          end
 
           node_hash[:hostname] = client.hostname
           [node_hash]
         end
 
         private
 
-        def node_attr attr, xml
-          xml_element(xml, "sysinfo/system/entry[@name='#{attr}']").strip
+        def sys_info
+          Nokogiri::XML(client.sys_info)
+        rescue LibvirtError
+          # qemu:///session typically doesn't have permission to retrieve this
+        rescue StandardError
+          # TODO: log this?
         end
       end
 

tests/libvirt/requests/compute/get_node_info_tests.rb

@@ -0,0 +1,14 @@
+Shindo.tests("Fog::Compute[:libvirt] | get_node_info", 'libvirt') do
+
+  compute = Fog::Compute[:libvirt]
+
+  tests("get_node_info response") do
+    response = compute.get_node_info
+    info = response[0]
+    tests("sys_info attributes") do
+      [:uuid, :manufacturer, :product, :serial].each do |attr|
+        test("attribute #{attr} is set") { info[attr].is_a?(String) }
+      end
+    end
+  end
+end