hyperv: use "is None" not "== None" for PEP-8 compliance

PEP 8 says:

    "Comparisons to singletons like None should always be done
     with 'is' or 'is not', never the equality operators."

There are potentially semantics differences, though in the case of this
libvirt code its merely a style change:

  http://jaredgrubb.blogspot.com/2009/04/python-is-none-vs-none.html

Reviewed-by: John Ferlan <jferlan@redhat.com>
Signed-off-by: Daniel P. Berrangé <berrange@redhat.com>

src/hyperv/hyperv_wmi_generator.py

@@ -65,7 +65,7 @@ class WmiClass:
         # because we'll generate "common" member and will be the "base" name
         if len(self.versions) > 1:
             first = self.versions[0]
-            if first.version == None:
+            if first.version is None:
                 first.version = "v1"
             first.name = "%s_%s" % (first.name, first.version)