Eliminate memory leak in xenUnifiedDomainInfoListFree

This fixes a leak described in

   https://bugzilla.redhat.com/show_bug.cgi?id=590073

xenUnifiedDomainInfoList has a pointer to a list of pointers to
xenUnifiedDomain. We were freeing up all the domains, but neglecting
to free the list.

This was found by Paolo Bonzini <pbonzini@redhat.com>.

src/xen/xen_driver.c

@@ -2044,6 +2044,7 @@ xenUnifiedDomainInfoListFree(xenUnifiedDomainInfoListPtr list)
         VIR_FREE(list->doms[i]->name);
         VIR_FREE(list->doms[i]);
     }
+    VIR_FREE(list->doms);
     VIR_FREE(list);
 }