news: Tweak existing v3.3.0 entries

Some of the content was not following the (loosely established)
style, and some of the XML was not aligned properly.

docs/news.xml

@@ -39,25 +39,25 @@
     <section title="Improvements">
       <change>
         <summary>
-          The libvirt Hyper-V driver now supports Hyper-V 2012 and newer.
+          hyperv: Support Hyper-V 2012 and newer
         </summary>
         <description>
           Starting with Hyper-V 2012 the API has changed causing the existing
           driver to be unable to send and process requests properly. This has
           been resolved by adding abstractions to handle the differences and
           ease handling such breaks if they happen in the future.
-       </description>
+        </description>
       </change>
       <change>
         <summary>
-          Add support for nested HVM domains in the libxl driver
+          libxl: Add support for nested HVM domains
         </summary>
         <description>
           Xen has supported nested HVM domains since version 4.4. The
           libvirt libxl driver now supports nested HVM domains by
           specifying the host-passthrough CPU mode when defining a
           domain.
-       </description>
+        </description>
       </change>
     </section>
     <section title="Bug fixes">